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 $165.64   11.247%   $184.2695   $184.27   $184.25   $184.30  
  Purchase #2 $141.61   8.226%   $153.2588   $153.26   $153.25   $153.30  
  Purchase #3 $61.60   5.281%   $64.8531   $64.85   $64.85   $64.90  
  Purchase #4 $208.90   3.502%   $216.2157   $216.22   $216.20   $216.20  
  Purchase #5 $24.87   9.247%   $27.1697   $27.17   $27.15   $27.20  
  Purchase #6 $179.94   12.719%   $202.8266   $202.83   $202.85   $202.80  
  Purchase #7 $102.85   8.701%   $111.799   $111.80   $111.80   $111.80  
  7 purchase totals = $885.41       $960.3924   $960.40   $960.35   $960.50