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 $209.84   5.779%   $221.9667   $221.97   $221.95   $222.00  
  Purchase #2 $226.74   6.165%   $240.7185   $240.72   $240.70   $240.70  
  Purchase #3 $243.67   7.635%   $262.2742   $262.27   $262.25   $262.30  
  Purchase #4 $94.81   13.186%   $107.3116   $107.31   $107.30   $107.30  
  Purchase #5 $195.39   11.767%   $218.3815   $218.38   $218.40   $218.40  
  Purchase #6 $92.36   13.338%   $104.679   $104.68   $104.70   $104.70  
  Purchase #7 $92.53   8.759%   $100.6347   $100.63   $100.65   $100.60  
  7 purchase totals = $1,155.34       $1,255.9662   $1,255.96   $1,255.95   $1,256.00