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 $108.29   10.378%   $119.5283   $119.53   $119.55   $119.50  
  Purchase #2 $67.94   5.310%   $71.5476   $71.55   $71.55   $71.50  
  Purchase #3 $76.90   4.330%   $80.2298   $80.23   $80.25   $80.20  
  Purchase #4 $176.42   11.778%   $197.1987   $197.20   $197.20   $197.20  
  Purchase #5 $23.92   12.148%   $26.8258   $26.83   $26.85   $26.80  
  Purchase #6 $94.34   8.551%   $102.407   $102.41   $102.40   $102.40  
  Purchase #7 $30.92   6.662%   $32.9799   $32.98   $33.00   $33.00  
  7 purchase totals = $578.73       $630.7171   $630.73   $630.80   $630.60