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 $72.81   4.721%   $76.2474   $76.25   $76.25   $76.20  
  Purchase #2 $69.45   11.808%   $77.6507   $77.65   $77.65   $77.70  
  Purchase #3 $154.27   11.139%   $171.4541   $171.45   $171.45   $171.50  
  Purchase #4 $72.56   4.663%   $75.9435   $75.94   $75.95   $75.90  
  Purchase #5 $228.82   5.563%   $241.5493   $241.55   $241.55   $241.50  
  Purchase #6 $173.98   4.635%   $182.044   $182.04   $182.05   $182.00  
  Purchase #7 $132.62   4.183%   $138.1675   $138.17   $138.15   $138.20  
  7 purchase totals = $904.51       $963.0565   $963.05   $963.05   $963.00