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 $60.65   4.419%   $63.3301   $63.33   $63.35   $63.30  
  Purchase #2 $195.33   3.547%   $202.2584   $202.26   $202.25   $202.30  
  Purchase #3 $84.81   11.369%   $94.452   $94.45   $94.45   $94.50  
  Purchase #4 $194.72   13.129%   $220.2848   $220.28   $220.30   $220.30  
  Purchase #5 $195.61   11.575%   $218.2519   $218.25   $218.25   $218.30  
  Purchase #6 $140.28   13.239%   $158.8517   $158.85   $158.85   $158.90  
  Purchase #7 $15.70   13.581%   $17.8322   $17.83   $17.85   $17.80  
  7 purchase totals = $887.10       $975.2611   $975.25   $975.30   $975.40