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 $115.88   12.666%   $130.5574   $130.56   $130.55   $130.60  
  Purchase #2 $227.97   8.469%   $247.2768   $247.28   $247.30   $247.30  
  Purchase #3 $63.34   5.771%   $66.9954   $67.00   $67.00   $67.00  
  Purchase #4 $243.87   13.390%   $276.5242   $276.52   $276.50   $276.50  
  Purchase #5 $39.66   6.402%   $42.199   $42.20   $42.20   $42.20  
  Purchase #6 $153.46   7.423%   $164.8513   $164.85   $164.85   $164.90  
  Purchase #7 $49.82   13.634%   $56.6125   $56.61   $56.60   $56.60  
  7 purchase totals = $894.00       $985.0166   $985.02   $985.00   $985.10