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 $25.41   7.372%   $27.2832   $27.28   $27.30   $27.30  
  Purchase #2 $207.57   4.370%   $216.6408   $216.64   $216.65   $216.60  
  Purchase #3 $157.83   7.157%   $169.1259   $169.13   $169.15   $169.10  
  Purchase #4 $125.43   8.623%   $136.2458   $136.25   $136.25   $136.20  
  Purchase #5 $140.59   6.575%   $149.8338   $149.83   $149.85   $149.80  
  Purchase #6 $239.30   11.118%   $265.9054   $265.91   $265.90   $265.90  
  Purchase #7 $142.46   8.512%   $154.5862   $154.59   $154.60   $154.60  
  7 purchase totals = $1,038.59       $1,119.6211   $1,119.63   $1,119.70   $1,119.50