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 $178.86   12.731%   $201.6307   $201.63   $201.65   $201.60  
  Purchase #2 $162.91   4.709%   $170.5814   $170.58   $170.60   $170.60  
  Purchase #3 $173.29   11.341%   $192.9428   $192.94   $192.95   $192.90  
  Purchase #4 $70.45   11.249%   $78.3749   $78.37   $78.35   $78.40  
  Purchase #5 $85.85   7.862%   $92.5995   $92.60   $92.60   $92.60  
  Purchase #6 $115.39   9.285%   $126.104   $126.10   $126.10   $126.10  
  Purchase #7 $79.62   9.354%   $87.0677   $87.07   $87.05   $87.10  
  7 purchase totals = $866.37       $949.3010   $949.29   $949.30   $949.30