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 $54.78   13.663%   $62.2646   $62.26   $62.25   $62.30  
  Purchase #2 $171.57   11.613%   $191.4944   $191.49   $191.50   $191.50  
  Purchase #3 $127.60   6.576%   $135.991   $135.99   $136.00   $136.00  
  Purchase #4 $243.32   5.382%   $256.4155   $256.42   $256.40   $256.40  
  Purchase #5 $135.73   11.434%   $151.2494   $151.25   $151.25   $151.20  
  Purchase #6 $122.41   3.301%   $126.4508   $126.45   $126.45   $126.50  
  Purchase #7 $139.86   4.200%   $145.7341   $145.73   $145.75   $145.70  
  7 purchase totals = $995.27       $1,069.5998   $1,069.59   $1,069.60   $1,069.60