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 $14.78   12.293%   $16.5969   $16.60   $16.60   $16.60  
  Purchase #2 $144.99   5.845%   $153.4647   $153.46   $153.45   $153.50  
  Purchase #3 $27.59   9.146%   $30.1134   $30.11   $30.10   $30.10  
  Purchase #4 $155.79   8.411%   $168.8935   $168.89   $168.90   $168.90  
  Purchase #5 $240.98   3.825%   $250.1975   $250.20   $250.20   $250.20  
  Purchase #6 $64.68   3.231%   $66.7698   $66.77   $66.75   $66.80  
  Purchase #7 $57.56   6.330%   $61.2035   $61.20   $61.20   $61.20  
  7 purchase totals = $706.37       $747.2393   $747.23   $747.20   $747.30