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 $234.29   13.190%   $265.1929   $265.19   $265.20   $265.20  
  Purchase #2 $211.78   8.571%   $229.9317   $229.93   $229.95   $229.90  
  Purchase #3 $134.67   7.623%   $144.9359   $144.94   $144.95   $144.90  
  Purchase #4 $92.55   4.661%   $96.8638   $96.86   $96.85   $96.90  
  Purchase #5 $244.73   10.574%   $270.6078   $270.61   $270.60   $270.60  
  Purchase #6 $59.59   8.146%   $64.4442   $64.44   $64.45   $64.40  
  Purchase #7 $74.91   6.494%   $79.7747   $79.77   $79.75   $79.80  
  7 purchase totals = $1,052.52       $1,151.7510   $1,151.74   $1,151.75   $1,151.70