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 $107.53   8.454%   $116.6206   $116.62   $116.60   $116.60  
  Purchase #2 $223.62   7.495%   $240.3803   $240.38   $240.40   $240.40  
  Purchase #3 $196.99   10.304%   $217.2878   $217.29   $217.30   $217.30  
  Purchase #4 $187.54   5.550%   $197.9485   $197.95   $197.95   $197.90  
  Purchase #5 $37.94   13.460%   $43.0467   $43.05   $43.05   $43.00  
  Purchase #6 $162.92   8.627%   $176.9751   $176.98   $177.00   $177.00  
  Purchase #7 $244.80   11.540%   $273.0499   $273.05   $273.05   $273.00  
  7 purchase totals = $1,161.34       $1,265.3089   $1,265.32   $1,265.35   $1,265.20