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 $220.89   10.606%   $244.3176   $244.32   $244.30   $244.30  
  Purchase #2 $12.53   12.548%   $14.1023   $14.10   $14.10   $14.10  
  Purchase #3 $74.67   7.819%   $80.5084   $80.51   $80.50   $80.50  
  Purchase #4 $229.27   11.576%   $255.8103   $255.81   $255.80   $255.80  
  Purchase #5 $224.74   3.646%   $232.934   $232.93   $232.95   $232.90  
  Purchase #6 $104.42   8.776%   $113.5839   $113.58   $113.60   $113.60  
  Purchase #7 $76.51   8.525%   $83.0325   $83.03   $83.05   $83.00  
  7 purchase totals = $943.03       $1,024.2890   $1,024.28   $1,024.30   $1,024.20