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 $113.43   10.485%   $125.3231   $125.32   $125.30   $125.30  
  Purchase #2 $87.25   7.645%   $93.9203   $93.92   $93.90   $93.90  
  Purchase #3 $151.27   6.826%   $161.5957   $161.60   $161.60   $161.60  
  Purchase #4 $89.58   11.636%   $100.0035   $100.00   $100.00   $100.00  
  Purchase #5 $221.90   8.652%   $241.0988   $241.10   $241.10   $241.10  
  Purchase #6 $88.73   6.305%   $94.3244   $94.32   $94.30   $94.30  
  Purchase #7 $199.40   4.124%   $207.6233   $207.62   $207.60   $207.60  
  7 purchase totals = $951.56       $1,023.8891   $1,023.88   $1,023.80   $1,023.80