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 $57.49   8.681%   $62.4807   $62.48   $62.50   $62.50  
  Purchase #2 $84.79   10.432%   $93.6353   $93.64   $93.65   $93.60  
  Purchase #3 $52.68   3.377%   $54.459   $54.46   $54.45   $54.50  
  Purchase #4 $85.84   6.609%   $91.5132   $91.51   $91.50   $91.50  
  Purchase #5 $214.97   13.494%   $243.9781   $243.98   $244.00   $244.00  
  Purchase #6 $6.93   13.750%   $7.8829   $7.88   $7.90   $7.90  
  Purchase #7 $98.97   3.592%   $102.525   $102.53   $102.55   $102.50  
  7 purchase totals = $601.67       $656.4742   $656.48   $656.55   $656.50