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 $241.37   9.610%   $264.5657   $264.57   $264.55   $264.60  
  Purchase #2 $92.73   5.755%   $98.0666   $98.07   $98.05   $98.10  
  Purchase #3 $67.74   5.860%   $71.7096   $71.71   $71.70   $71.70  
  Purchase #4 $15.45   7.219%   $16.5653   $16.57   $16.55   $16.60  
  Purchase #5 $18.82   4.423%   $19.6524   $19.65   $19.65   $19.70  
  Purchase #6 $225.80   9.656%   $247.6032   $247.60   $247.60   $247.60  
  Purchase #7 $199.57   8.642%   $216.8168   $216.82   $216.80   $216.80  
  7 purchase totals = $861.48       $934.9796   $934.99   $934.90   $935.10