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 $82.64   11.744%   $92.3452   $92.35   $92.35   $92.30  
  Purchase #2 $22.87   7.796%   $24.6529   $24.65   $24.65   $24.70  
  Purchase #3 $134.58   5.395%   $141.8406   $141.84   $141.85   $141.80  
  Purchase #4 $134.78   4.266%   $140.5297   $140.53   $140.55   $140.50  
  Purchase #5 $92.44   12.804%   $104.276   $104.28   $104.30   $104.30  
  Purchase #6 $248.82   12.375%   $279.6115   $279.61   $279.60   $279.60  
  Purchase #7 $45.83   9.243%   $50.0661   $50.07   $50.05   $50.10  
  7 purchase totals = $761.96       $833.3220   $833.33   $833.35   $833.30