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 $31.88   12.798%   $35.96   $35.96   $35.95   $36.00  
  Purchase #2 $122.54   3.196%   $126.4564   $126.46   $126.45   $126.50  
  Purchase #3 $237.90   11.232%   $264.6209   $264.62   $264.60   $264.60  
  Purchase #4 $26.96   10.832%   $29.8803   $29.88   $29.90   $29.90  
  Purchase #5 $210.33   8.152%   $227.4761   $227.48   $227.50   $227.50  
  Purchase #6 $44.77   3.383%   $46.2846   $46.28   $46.30   $46.30  
  Purchase #7 $84.38   11.383%   $93.985   $93.99   $94.00   $94.00  
  7 purchase totals = $758.76       $824.6633   $824.67   $824.70   $824.80