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 $194.32   4.260%   $202.598   $202.60   $202.60   $202.60  
  Purchase #2 $82.89   5.684%   $87.6015   $87.60   $87.60   $87.60  
  Purchase #3 $35.47   8.136%   $38.3558   $38.36   $38.35   $38.40  
  Purchase #4 $58.66   4.800%   $61.4757   $61.48   $61.50   $61.50  
  Purchase #5 $150.55   8.166%   $162.8439   $162.84   $162.85   $162.80  
  Purchase #6 $94.79   13.131%   $107.2369   $107.24   $107.25   $107.20  
  Purchase #7 $214.53   12.134%   $240.5611   $240.56   $240.55   $240.60  
  7 purchase totals = $831.21       $900.6729   $900.68   $900.70   $900.70