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 $53.49   8.355%   $57.9591   $57.96   $57.95   $58.00  
  Purchase #2 $192.27   9.737%   $210.9913   $210.99   $211.00   $211.00  
  Purchase #3 $144.41   12.170%   $161.9847   $161.98   $162.00   $162.00  
  Purchase #4 $58.89   9.130%   $64.2667   $64.27   $64.25   $64.30  
  Purchase #5 $168.25   4.596%   $175.9828   $175.98   $176.00   $176.00  
  Purchase #6 $126.86   6.504%   $135.111   $135.11   $135.10   $135.10  
  Purchase #7 $68.68   13.545%   $77.9827   $77.98   $78.00   $78.00  
  7 purchase totals = $812.85       $884.2783   $884.27   $884.30   $884.40