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 $195.84   9.638%   $214.7151   $214.72   $214.70   $214.70  
  Purchase #2 $168.98   6.611%   $180.1513   $180.15   $180.15   $180.20  
  Purchase #3 $219.98   12.459%   $247.3873   $247.39   $247.40   $247.40  
  Purchase #4 $60.54   11.582%   $67.5517   $67.55   $67.55   $67.60  
  Purchase #5 $117.70   5.673%   $124.3771   $124.38   $124.40   $124.40  
  Purchase #6 $18.78   13.404%   $21.2973   $21.30   $21.30   $21.30  
  Purchase #7 $150.25   10.215%   $165.598   $165.60   $165.60   $165.60  
  7 purchase totals = $932.07       $1,021.0778   $1,021.09   $1,021.10   $1,021.20