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 $221.71   8.712%   $241.0254   $241.03   $241.05   $241.00  
  Purchase #2 $206.77   3.148%   $213.2791   $213.28   $213.30   $213.30  
  Purchase #3 $184.85   7.511%   $198.7341   $198.73   $198.75   $198.70  
  Purchase #4 $132.82   12.680%   $149.6616   $149.66   $149.65   $149.70  
  Purchase #5 $194.54   8.865%   $211.786   $211.79   $211.80   $211.80  
  Purchase #6 $191.25   9.718%   $209.8357   $209.84   $209.85   $209.80  
  Purchase #7 $93.97   5.868%   $99.4842   $99.48   $99.50   $99.50  
  7 purchase totals = $1,225.91       $1,323.8061   $1,323.81   $1,323.90   $1,323.80