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 $244.41   6.436%   $260.1402   $260.14   $260.15   $260.10  
  Purchase #2 $58.71   5.177%   $61.7494   $61.75   $61.75   $61.70  
  Purchase #3 $19.42   4.717%   $20.336   $20.34   $20.35   $20.30  
  Purchase #4 $55.49   7.495%   $59.649   $59.65   $59.65   $59.60  
  Purchase #5 $163.88   9.359%   $179.2175   $179.22   $179.20   $179.20  
  Purchase #6 $177.50   8.269%   $192.1775   $192.18   $192.20   $192.20  
  Purchase #7 $234.73   6.198%   $249.2786   $249.28   $249.30   $249.30  
  7 purchase totals = $954.14       $1,022.5482   $1,022.56   $1,022.60   $1,022.40