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 $65.77   10.120%   $72.4259   $72.43   $72.45   $72.40  
  Purchase #2 $105.41   4.595%   $110.2536   $110.25   $110.25   $110.30  
  Purchase #3 $199.93   5.461%   $210.8482   $210.85   $210.85   $210.80  
  Purchase #4 $13.99   10.412%   $15.4466   $15.45   $15.45   $15.40  
  Purchase #5 $163.26   13.846%   $185.865   $185.87   $185.85   $185.90  
  Purchase #6 $84.57   10.632%   $93.5615   $93.56   $93.55   $93.60  
  Purchase #7 $147.45   13.272%   $167.0196   $167.02   $167.00   $167.00  
  7 purchase totals = $780.38       $855.4204   $855.43   $855.40   $855.40