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 $127.94   8.358%   $138.6332   $138.63   $138.65   $138.60  
  Purchase #2 $9.36   13.349%   $10.6095   $10.61   $10.60   $10.60  
  Purchase #3 $66.28   13.594%   $75.2901   $75.29   $75.30   $75.30  
  Purchase #4 $59.65   6.513%   $63.535   $63.54   $63.55   $63.50  
  Purchase #5 $245.45   11.748%   $274.2855   $274.29   $274.30   $274.30  
  Purchase #6 $109.33   4.454%   $114.1996   $114.20   $114.20   $114.20  
  Purchase #7 $51.37   9.593%   $56.2979   $56.30   $56.30   $56.30  
  7 purchase totals = $669.38       $732.8508   $732.86   $732.90   $732.80