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 $54.71   10.126%   $60.2499   $60.25   $60.25   $60.20  
  Purchase #2 $213.98   8.707%   $232.6112   $232.61   $232.60   $232.60  
  Purchase #3 $111.97   6.212%   $118.9256   $118.93   $118.95   $118.90  
  Purchase #4 $220.51   5.217%   $232.014   $232.01   $232.00   $232.00  
  Purchase #5 $194.42   7.381%   $208.7701   $208.77   $208.75   $208.80  
  Purchase #6 $32.94   12.243%   $36.9728   $36.97   $36.95   $37.00  
  Purchase #7 $45.90   10.556%   $50.7452   $50.75   $50.75   $50.70  
  7 purchase totals = $874.43       $940.2888   $940.29   $940.25   $940.20