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 $61.96   6.454%   $65.9589   $65.96   $65.95   $66.00  
  Purchase #2 $154.38   12.501%   $173.679   $173.68   $173.70   $173.70  
  Purchase #3 $143.31   3.851%   $148.8289   $148.83   $148.85   $148.80  
  Purchase #4 $38.92   4.830%   $40.7998   $40.80   $40.80   $40.80  
  Purchase #5 $44.56   4.508%   $46.5688   $46.57   $46.55   $46.60  
  Purchase #6 $248.77   5.639%   $262.7981   $262.80   $262.80   $262.80  
  Purchase #7 $149.89   8.559%   $162.7191   $162.72   $162.70   $162.70  
  7 purchase totals = $841.79       $901.3526   $901.36   $901.35   $901.40