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 $29.76   7.686%   $32.0474   $32.05   $32.05   $32.00  
  Purchase #2 $54.65   6.129%   $57.9995   $58.00   $58.00   $58.00  
  Purchase #3 $161.94   9.130%   $176.7251   $176.73   $176.75   $176.70  
  Purchase #4 $214.95   13.617%   $244.2197   $244.22   $244.20   $244.20  
  Purchase #5 $215.82   8.348%   $233.8367   $233.84   $233.85   $233.80  
  Purchase #6 $57.50   10.612%   $63.6019   $63.60   $63.60   $63.60  
  Purchase #7 $142.83   13.811%   $162.5563   $162.56   $162.55   $162.60  
  7 purchase totals = $877.45       $970.9866   $971.00   $971.00   $970.90