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 $237.83   11.111%   $264.2553   $264.26   $264.25   $264.30  
  Purchase #2 $204.68   12.782%   $230.8422   $230.84   $230.85   $230.80  
  Purchase #3 $20.33   13.746%   $23.1246   $23.12   $23.10   $23.10  
  Purchase #4 $98.79   12.756%   $111.3917   $111.39   $111.40   $111.40  
  Purchase #5 $200.27   8.174%   $216.6401   $216.64   $216.65   $216.60  
  Purchase #6 $93.79   4.513%   $98.0227   $98.02   $98.00   $98.00  
  Purchase #7 $76.98   8.226%   $83.3124   $83.31   $83.30   $83.30  
  7 purchase totals = $932.67       $1,027.5890   $1,027.58   $1,027.55   $1,027.50