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 $71.30   6.413%   $75.8725   $75.87   $75.85   $75.90  
  Purchase #2 $15.55   10.106%   $17.1215   $17.12   $17.10   $17.10  
  Purchase #3 $221.40   10.187%   $243.954   $243.95   $243.95   $244.00  
  Purchase #4 $108.73   11.129%   $120.8306   $120.83   $120.85   $120.80  
  Purchase #5 $116.84   9.341%   $127.754   $127.75   $127.75   $127.80  
  Purchase #6 $133.75   11.120%   $148.623   $148.62   $148.60   $148.60  
  Purchase #7 $131.75   6.346%   $140.1109   $140.11   $140.10   $140.10  
  7 purchase totals = $799.32       $874.2665   $874.25   $874.20   $874.30