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 $166.86   11.252%   $185.6351   $185.64   $185.65   $185.60  
  Purchase #2 $23.53   5.113%   $24.7331   $24.73   $24.75   $24.70  
  Purchase #3 $59.84   4.786%   $62.7039   $62.70   $62.70   $62.70  
  Purchase #4 $39.97   7.863%   $43.1128   $43.11   $43.10   $43.10  
  Purchase #5 $32.28   11.402%   $35.9606   $35.96   $35.95   $36.00  
  Purchase #6 $201.38   7.729%   $216.9447   $216.94   $216.95   $216.90  
  Purchase #7 $137.81   7.668%   $148.3773   $148.38   $148.40   $148.40  
  7 purchase totals = $661.67       $717.4675   $717.46   $717.50   $717.40