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 $46.67   13.231%   $52.8449   $52.84   $52.85   $52.80  
  Purchase #2 $180.46   13.128%   $204.1508   $204.15   $204.15   $204.20  
  Purchase #3 $167.99   8.567%   $182.3817   $182.38   $182.40   $182.40  
  Purchase #4 $149.42   3.428%   $154.5421   $154.54   $154.55   $154.50  
  Purchase #5 $185.81   12.107%   $208.306   $208.31   $208.30   $208.30  
  Purchase #6 $207.86   6.686%   $221.7575   $221.76   $221.75   $221.80  
  Purchase #7 $219.29   11.179%   $243.8044   $243.80   $243.80   $243.80  
  7 purchase totals = $1,157.50       $1,267.7874   $1,267.78   $1,267.80   $1,267.80