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 $140.74   12.413%   $158.2101   $158.21   $158.20   $158.20  
  Purchase #2 $199.67   3.667%   $206.9919   $206.99   $207.00   $207.00  
  Purchase #3 $85.79   10.271%   $94.6015   $94.60   $94.60   $94.60  
  Purchase #4 $156.69   12.433%   $176.1713   $176.17   $176.15   $176.20  
  Purchase #5 $216.48   7.453%   $232.6143   $232.61   $232.60   $232.60  
  Purchase #6 $247.68   9.646%   $271.5712   $271.57   $271.55   $271.60  
  Purchase #7 $199.98   13.434%   $226.8453   $226.85   $226.85   $226.80  
  7 purchase totals = $1,247.03       $1,367.0056   $1,367.00   $1,366.95   $1,367.00