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 $78.81   5.632%   $83.2486   $83.25   $83.25   $83.20  
  Purchase #2 $128.99   8.867%   $140.4275   $140.43   $140.45   $140.40  
  Purchase #3 $249.39   7.333%   $267.6778   $267.68   $267.70   $267.70  
  Purchase #4 $127.75   6.593%   $136.1726   $136.17   $136.15   $136.20  
  Purchase #5 $50.46   11.582%   $56.3043   $56.30   $56.30   $56.30  
  Purchase #6 $58.71   10.479%   $64.8622   $64.86   $64.85   $64.90  
  Purchase #7 $249.63   8.768%   $271.5176   $271.52   $271.50   $271.50  
  7 purchase totals = $943.74       $1,020.2106   $1,020.21   $1,020.20   $1,020.20