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 $46.28   4.562%   $48.3913   $48.39   $48.40   $48.40  
  Purchase #2 $223.79   13.799%   $254.6708   $254.67   $254.65   $254.70  
  Purchase #3 $54.84   12.557%   $61.7263   $61.73   $61.75   $61.70  
  Purchase #4 $156.73   13.873%   $178.4732   $178.47   $178.45   $178.50  
  Purchase #5 $148.89   9.124%   $162.4747   $162.47   $162.45   $162.50  
  Purchase #6 $213.89   11.817%   $239.1654   $239.17   $239.15   $239.20  
  Purchase #7 $17.92   10.441%   $19.791   $19.79   $19.80   $19.80  
  7 purchase totals = $862.34       $964.6927   $964.69   $964.65   $964.80