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 $173.53   12.171%   $194.6503   $194.65   $194.65   $194.70  
  Purchase #2 $16.78   12.421%   $18.8642   $18.86   $18.85   $18.90  
  Purchase #3 $249.66   3.259%   $257.7964   $257.80   $257.80   $257.80  
  Purchase #4 $119.29   4.733%   $124.936   $124.94   $124.95   $124.90  
  Purchase #5 $191.49   3.420%   $198.039   $198.04   $198.05   $198.00  
  Purchase #6 $239.62   7.743%   $258.1738   $258.17   $258.15   $258.20  
  Purchase #7 $64.79   6.447%   $68.967   $68.97   $68.95   $69.00  
  7 purchase totals = $1,055.16       $1,121.4267   $1,121.43   $1,121.40   $1,121.50