Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.97   10.720%   $261.266   $261.27   $261.25   $261.30  
  Purchase #2 $95.61   11.440%   $106.5478   $106.55   $106.55   $106.50  
  Purchase #3 $233.44   10.744%   $258.5208   $258.52   $258.50   $258.50  
  Purchase #4 $240.74   10.767%   $266.6605   $266.66   $266.65   $266.70  
  Purchase #5 $125.49   8.129%   $135.6911   $135.69   $135.70   $135.70  
  Purchase #6 $132.35   13.224%   $149.852   $149.85   $149.85   $149.90  
  Purchase #7 $126.30   7.645%   $135.9556   $135.96   $135.95   $136.00  
  7 purchase totals = $1,189.90       $1,314.4938   $1,314.50   $1,314.45   $1,314.60