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 $245.75   7.843%   $265.0242   $265.02   $265.00   $265.00  
  Purchase #2 $182.58   9.122%   $199.2349   $199.23   $199.25   $199.20  
  Purchase #3 $231.32   10.495%   $255.597   $255.60   $255.60   $255.60  
  Purchase #4 $108.46   3.550%   $112.3103   $112.31   $112.30   $112.30  
  Purchase #5 $100.51   8.160%   $108.7116   $108.71   $108.70   $108.70  
  Purchase #6 $235.86   3.852%   $244.9453   $244.95   $244.95   $244.90  
  Purchase #7 $166.34   9.729%   $182.5232   $182.52   $182.50   $182.50  
  7 purchase totals = $1,270.82       $1,368.3465   $1,368.34   $1,368.30   $1,368.20