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 $55.43   4.539%   $57.946   $57.95   $57.95   $57.90  
  Purchase #2 $45.60   13.240%   $51.6374   $51.64   $51.65   $51.60  
  Purchase #3 $65.29   7.319%   $70.0686   $70.07   $70.05   $70.10  
  Purchase #4 $237.64   6.541%   $253.184   $253.18   $253.20   $253.20  
  Purchase #5 $246.68   13.446%   $279.8486   $279.85   $279.85   $279.80  
  Purchase #6 $61.42   11.266%   $68.3396   $68.34   $68.35   $68.30  
  Purchase #7 $129.78   9.843%   $142.5542   $142.55   $142.55   $142.60  
  7 purchase totals = $841.84       $923.5784   $923.58   $923.60   $923.50