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 $227.26   8.347%   $246.2294   $246.23   $246.25   $246.20  
  Purchase #2 $22.53   5.707%   $23.8158   $23.82   $23.80   $23.80  
  Purchase #3 $201.28   8.289%   $217.9641   $217.96   $217.95   $218.00  
  Purchase #4 $245.42   4.291%   $255.951   $255.95   $255.95   $256.00  
  Purchase #5 $97.84   10.124%   $107.7453   $107.75   $107.75   $107.70  
  Purchase #6 $122.48   13.717%   $139.2806   $139.28   $139.30   $139.30  
  Purchase #7 $60.93   13.673%   $69.261   $69.26   $69.25   $69.30  
  7 purchase totals = $977.74       $1,060.2472   $1,060.25   $1,060.25   $1,060.30