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 $86.36   12.486%   $97.1429   $97.14   $97.15   $97.10  
  Purchase #2 $245.89   9.204%   $268.5217   $268.52   $268.50   $268.50  
  Purchase #3 $51.47   10.678%   $56.966   $56.97   $56.95   $57.00  
  Purchase #4 $91.57   12.310%   $102.8423   $102.84   $102.85   $102.80  
  Purchase #5 $210.63   7.815%   $227.0907   $227.09   $227.10   $227.10  
  Purchase #6 $132.67   7.364%   $142.4398   $142.44   $142.45   $142.40  
  Purchase #7 $130.66   9.389%   $142.9277   $142.93   $142.95   $142.90  
  7 purchase totals = $949.25       $1,037.9311   $1,037.93   $1,037.95   $1,037.80