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 $177.78   10.825%   $197.0247   $197.02   $197.00   $197.00  
  Purchase #2 $209.89   9.478%   $229.7834   $229.78   $229.80   $229.80  
  Purchase #3 $106.73   7.171%   $114.3836   $114.38   $114.40   $114.40  
  Purchase #4 $66.72   6.794%   $71.253   $71.25   $71.25   $71.30  
  Purchase #5 $210.88   5.673%   $222.8432   $222.84   $222.85   $222.80  
  Purchase #6 $39.61   7.761%   $42.6841   $42.68   $42.70   $42.70  
  Purchase #7 $233.26   8.850%   $253.9035   $253.90   $253.90   $253.90  
  7 purchase totals = $1,044.87       $1,131.8755   $1,131.85   $1,131.90   $1,131.90