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 $63.45   10.277%   $69.9708   $69.97   $69.95   $70.00  
  Purchase #2 $88.44   4.405%   $92.3358   $92.34   $92.35   $92.30  
  Purchase #3 $88.73   4.627%   $92.8355   $92.84   $92.85   $92.80  
  Purchase #4 $220.31   9.837%   $241.9819   $241.98   $242.00   $242.00  
  Purchase #5 $161.30   12.840%   $182.0109   $182.01   $182.00   $182.00  
  Purchase #6 $215.96   12.172%   $242.2467   $242.25   $242.25   $242.20  
  Purchase #7 $36.61   13.517%   $41.5586   $41.56   $41.55   $41.60  
  7 purchase totals = $874.80       $962.9402   $962.95   $962.95   $962.90