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 $62.47   11.661%   $69.7546   $69.75   $69.75   $69.80  
  Purchase #2 $156.37   6.383%   $166.3511   $166.35   $166.35   $166.40  
  Purchase #3 $47.86   13.474%   $54.3087   $54.31   $54.30   $54.30  
  Purchase #4 $127.55   4.521%   $133.3165   $133.32   $133.30   $133.30  
  Purchase #5 $233.30   10.370%   $257.4932   $257.49   $257.50   $257.50  
  Purchase #6 $116.51   4.337%   $121.563   $121.56   $121.55   $121.60  
  Purchase #7 $168.35   5.712%   $177.9662   $177.97   $177.95   $178.00  
  7 purchase totals = $912.41       $980.7533   $980.75   $980.70   $980.90