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 $119.81   11.167%   $133.1892   $133.19   $133.20   $133.20  
  Purchase #2 $235.47   12.739%   $265.4665   $265.47   $265.45   $265.50  
  Purchase #3 $65.57   6.604%   $69.9002   $69.90   $69.90   $69.90  
  Purchase #4 $130.95   6.261%   $139.1488   $139.15   $139.15   $139.10  
  Purchase #5 $49.45   12.257%   $55.5111   $55.51   $55.50   $55.50  
  Purchase #6 $171.94   12.608%   $193.6182   $193.62   $193.60   $193.60  
  Purchase #7 $90.51   4.243%   $94.3503   $94.35   $94.35   $94.40  
  7 purchase totals = $863.70       $951.1843   $951.19   $951.15   $951.20