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 $236.88   10.726%   $262.2877   $262.29   $262.30   $262.30  
  Purchase #2 $121.68   3.124%   $125.4813   $125.48   $125.50   $125.50  
  Purchase #3 $158.77   4.319%   $165.6273   $165.63   $165.65   $165.60  
  Purchase #4 $248.91   11.634%   $277.8682   $277.87   $277.85   $277.90  
  Purchase #5 $37.92   3.437%   $39.2233   $39.22   $39.20   $39.20  
  Purchase #6 $243.77   7.118%   $261.1215   $261.12   $261.10   $261.10  
  Purchase #7 $53.40   11.606%   $59.5976   $59.60   $59.60   $59.60  
  7 purchase totals = $1,101.33       $1,191.2069   $1,191.21   $1,191.20   $1,191.20