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 $59.51   3.248%   $61.4429   $61.44   $61.45   $61.40  
  Purchase #2 $93.57   8.869%   $101.8687   $101.87   $101.85   $101.90  
  Purchase #3 $218.41   11.413%   $243.3371   $243.34   $243.35   $243.30  
  Purchase #4 $210.64   7.439%   $226.3095   $226.31   $226.30   $226.30  
  Purchase #5 $188.75   10.134%   $207.8779   $207.88   $207.90   $207.90  
  Purchase #6 $34.47   10.452%   $38.0728   $38.07   $38.05   $38.10  
  Purchase #7 $95.76   7.604%   $103.0416   $103.04   $103.05   $103.00  
  7 purchase totals = $901.11       $981.9505   $981.95   $981.95   $981.90