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 $69.96   13.389%   $79.3269   $79.33   $79.35   $79.30  
  Purchase #2 $15.97   4.871%   $16.7479   $16.75   $16.75   $16.70  
  Purchase #3 $9.37   11.608%   $10.4577   $10.46   $10.45   $10.50  
  Purchase #4 $90.85   5.656%   $95.9885   $95.99   $96.00   $96.00  
  Purchase #5 $179.38   7.809%   $193.3878   $193.39   $193.40   $193.40  
  Purchase #6 $146.77   3.376%   $151.725   $151.73   $151.75   $151.70  
  Purchase #7 $54.79   6.794%   $58.5124   $58.51   $58.50   $58.50  
  7 purchase totals = $567.09       $606.1462   $606.16   $606.20   $606.10