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 $181.49   12.491%   $204.1599   $204.16   $204.15   $204.20  
  Purchase #2 $48.91   10.324%   $53.9595   $53.96   $53.95   $54.00  
  Purchase #3 $35.28   13.539%   $40.0566   $40.06   $40.05   $40.10  
  Purchase #4 $151.99   4.674%   $159.094   $159.09   $159.10   $159.10  
  Purchase #5 $241.93   10.216%   $266.6456   $266.65   $266.65   $266.60  
  Purchase #6 $194.98   8.179%   $210.9274   $210.93   $210.95   $210.90  
  Purchase #7 $140.63   12.845%   $158.6939   $158.69   $158.70   $158.70  
  7 purchase totals = $995.21       $1,093.5369   $1,093.54   $1,093.55   $1,093.60