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 $186.59   8.209%   $201.9072   $201.91   $201.90   $201.90  
  Purchase #2 $196.84   4.240%   $205.186   $205.19   $205.20   $205.20  
  Purchase #3 $46.75   9.564%   $51.2212   $51.22   $51.20   $51.20  
  Purchase #4 $224.78   6.403%   $239.1727   $239.17   $239.15   $239.20  
  Purchase #5 $5.25   9.535%   $5.7506   $5.75   $5.75   $5.80  
  Purchase #6 $62.94   12.604%   $70.873   $70.87   $70.85   $70.90  
  Purchase #7 $47.51   13.656%   $53.998   $54.00   $54.00   $54.00  
  7 purchase totals = $770.66       $828.1087   $828.11   $828.05   $828.20