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 $194.63   6.733%   $207.7344   $207.73   $207.75   $207.70  
  Purchase #2 $68.75   13.208%   $77.8305   $77.83   $77.85   $77.80  
  Purchase #3 $21.83   3.683%   $22.634   $22.63   $22.65   $22.60  
  Purchase #4 $139.28   11.749%   $155.644   $155.64   $155.65   $155.60  
  Purchase #5 $205.62   6.439%   $218.8599   $218.86   $218.85   $218.90  
  Purchase #6 $24.48   3.107%   $25.2406   $25.24   $25.25   $25.20  
  Purchase #7 $250.65   7.769%   $270.123   $270.12   $270.10   $270.10  
  7 purchase totals = $905.24       $978.0664   $978.05   $978.10   $977.90