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 $205.85   13.317%   $233.263   $233.26   $233.25   $233.30  
  Purchase #2 $119.78   10.226%   $132.0287   $132.03   $132.05   $132.00  
  Purchase #3 $68.62   11.692%   $76.6431   $76.64   $76.65   $76.60  
  Purchase #4 $215.89   12.624%   $243.144   $243.14   $243.15   $243.10  
  Purchase #5 $119.82   8.515%   $130.0227   $130.02   $130.00   $130.00  
  Purchase #6 $36.55   13.396%   $41.4462   $41.45   $41.45   $41.40  
  Purchase #7 $250.72   5.657%   $264.9032   $264.90   $264.90   $264.90  
  7 purchase totals = $1,017.23       $1,121.4509   $1,121.44   $1,121.45   $1,121.30