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 $92.58   6.165%   $98.2876   $98.29   $98.30   $98.30  
  Purchase #2 $240.79   11.863%   $269.3549   $269.35   $269.35   $269.40  
  Purchase #3 $104.97   12.279%   $117.8593   $117.86   $117.85   $117.90  
  Purchase #4 $176.49   10.308%   $194.6826   $194.68   $194.70   $194.70  
  Purchase #5 $22.99   3.550%   $23.8061   $23.81   $23.80   $23.80  
  Purchase #6 $40.91   9.302%   $44.7154   $44.72   $44.70   $44.70  
  Purchase #7 $55.73   11.409%   $62.0882   $62.09   $62.10   $62.10  
  7 purchase totals = $734.46       $810.7941   $810.80   $810.80   $810.90