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 $237.44   13.266%   $268.9388   $268.94   $268.95   $268.90  
  Purchase #2 $244.92   4.566%   $256.103   $256.10   $256.10   $256.10  
  Purchase #3 $45.43   13.231%   $51.4408   $51.44   $51.45   $51.40  
  Purchase #4 $64.89   10.468%   $71.6827   $71.68   $71.70   $71.70  
  Purchase #5 $56.83   3.399%   $58.7617   $58.76   $58.75   $58.80  
  Purchase #6 $103.71   4.447%   $108.322   $108.32   $108.30   $108.30  
  Purchase #7 $192.97   12.437%   $216.9697   $216.97   $216.95   $217.00  
  7 purchase totals = $946.19       $1,032.2187   $1,032.21   $1,032.20   $1,032.20