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 $134.67   4.871%   $141.2298   $141.23   $141.25   $141.20  
  Purchase #2 $68.87   9.265%   $75.2508   $75.25   $75.25   $75.30  
  Purchase #3 $128.97   10.346%   $142.3132   $142.31   $142.30   $142.30  
  Purchase #4 $56.40   3.310%   $58.2668   $58.27   $58.25   $58.30  
  Purchase #5 $109.67   4.710%   $114.8355   $114.84   $114.85   $114.80  
  Purchase #6 $191.83   11.559%   $214.0036   $214.00   $214.00   $214.00  
  Purchase #7 $114.92   8.455%   $124.6365   $124.64   $124.65   $124.60  
  7 purchase totals = $805.33       $870.5362   $870.54   $870.55   $870.50