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 $16.41   8.242%   $17.7625   $17.76   $17.75   $17.80  
  Purchase #2 $58.42   5.615%   $61.7003   $61.70   $61.70   $61.70  
  Purchase #3 $158.65   12.772%   $178.9128   $178.91   $178.90   $178.90  
  Purchase #4 $80.82   12.850%   $91.2054   $91.21   $91.20   $91.20  
  Purchase #5 $45.97   9.815%   $50.482   $50.48   $50.50   $50.50  
  Purchase #6 $137.41   10.293%   $151.5536   $151.55   $151.55   $151.60  
  Purchase #7 $200.91   3.201%   $207.3411   $207.34   $207.35   $207.30  
  7 purchase totals = $698.59       $758.9577   $758.95   $758.95   $759.00