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 $65.82   12.408%   $73.9869   $73.99   $74.00   $74.00  
  Purchase #2 $239.55   11.514%   $267.1318   $267.13   $267.15   $267.10  
  Purchase #3 $117.45   5.824%   $124.2903   $124.29   $124.30   $124.30  
  Purchase #4 $204.44   13.627%   $232.299   $232.30   $232.30   $232.30  
  Purchase #5 $238.55   12.304%   $267.9012   $267.90   $267.90   $267.90  
  Purchase #6 $22.74   4.781%   $23.8272   $23.83   $23.85   $23.80  
  Purchase #7 $186.37   5.116%   $195.9047   $195.90   $195.90   $195.90  
  7 purchase totals = $1,074.92       $1,185.3411   $1,185.34   $1,185.40   $1,185.30