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 $209.49   12.424%   $235.517   $235.52   $235.50   $235.50  
  Purchase #2 $41.76   6.857%   $44.6235   $44.62   $44.60   $44.60  
  Purchase #3 $226.44   12.589%   $254.9465   $254.95   $254.95   $254.90  
  Purchase #4 $203.46   5.165%   $213.9687   $213.97   $213.95   $214.00  
  Purchase #5 $243.81   12.345%   $273.9083   $273.91   $273.90   $273.90  
  Purchase #6 $216.49   13.862%   $246.4998   $246.50   $246.50   $246.50  
  Purchase #7 $158.94   3.463%   $164.4441   $164.44   $164.45   $164.40  
  7 purchase totals = $1,300.39       $1,433.9079   $1,433.91   $1,433.85   $1,433.80