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 $112.60   6.298%   $119.6915   $119.69   $119.70   $119.70  
  Purchase #2 $51.33   8.695%   $55.7931   $55.79   $55.80   $55.80  
  Purchase #3 $79.92   10.486%   $88.3004   $88.30   $88.30   $88.30  
  Purchase #4 $87.36   8.650%   $94.9166   $94.92   $94.90   $94.90  
  Purchase #5 $172.85   11.750%   $193.1599   $193.16   $193.15   $193.20  
  Purchase #6 $249.69   10.311%   $275.4355   $275.44   $275.45   $275.40  
  Purchase #7 $178.96   10.221%   $197.2515   $197.25   $197.25   $197.30  
  7 purchase totals = $932.71       $1,024.5485   $1,024.55   $1,024.55   $1,024.60