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 $43.44   13.315%   $49.224   $49.22   $49.20   $49.20  
  Purchase #2 $60.96   5.480%   $64.3006   $64.30   $64.30   $64.30  
  Purchase #3 $75.76   13.664%   $86.1118   $86.11   $86.10   $86.10  
  Purchase #4 $161.26   3.821%   $167.4217   $167.42   $167.40   $167.40  
  Purchase #5 $210.63   11.387%   $234.6144   $234.61   $234.60   $234.60  
  Purchase #6 $220.66   12.239%   $247.6666   $247.67   $247.65   $247.70  
  Purchase #7 $140.55   5.426%   $148.1762   $148.18   $148.20   $148.20  
  7 purchase totals = $913.26       $997.5153   $997.51   $997.45   $997.50