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 $128.57   6.179%   $136.5143   $136.51   $136.50   $136.50  
  Purchase #2 $227.44   6.245%   $241.6436   $241.64   $241.65   $241.60  
  Purchase #3 $24.64   7.590%   $26.5102   $26.51   $26.50   $26.50  
  Purchase #4 $160.63   6.629%   $171.2782   $171.28   $171.30   $171.30  
  Purchase #5 $100.32   6.214%   $106.5539   $106.55   $106.55   $106.60  
  Purchase #6 $147.38   8.800%   $160.3494   $160.35   $160.35   $160.30  
  Purchase #7 $74.96   11.280%   $83.4155   $83.42   $83.40   $83.40  
  7 purchase totals = $863.94       $926.2651   $926.26   $926.25   $926.20