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 $82.56   11.840%   $92.3351   $92.34   $92.35   $92.30  
  Purchase #2 $219.89   3.448%   $227.4718   $227.47   $227.45   $227.50  
  Purchase #3 $53.94   12.271%   $60.559   $60.56   $60.55   $60.60  
  Purchase #4 $122.47   11.716%   $136.8186   $136.82   $136.80   $136.80  
  Purchase #5 $222.40   11.423%   $247.8048   $247.80   $247.80   $247.80  
  Purchase #6 $203.48   6.255%   $216.2077   $216.21   $216.20   $216.20  
  Purchase #7 $22.54   3.369%   $23.2994   $23.30   $23.30   $23.30  
  7 purchase totals = $927.28       $1,004.4964   $1,004.50   $1,004.45   $1,004.50