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 $65.61   8.684%   $71.3076   $71.31   $71.30   $71.30  
  Purchase #2 $57.78   5.355%   $60.8741   $60.87   $60.85   $60.90  
  Purchase #3 $214.94   11.565%   $239.7978   $239.80   $239.80   $239.80  
  Purchase #4 $78.66   11.663%   $87.8341   $87.83   $87.85   $87.80  
  Purchase #5 $163.73   8.469%   $177.5963   $177.60   $177.60   $177.60  
  Purchase #6 $81.44   4.166%   $84.8328   $84.83   $84.85   $84.80  
  Purchase #7 $10.34   8.448%   $11.2135   $11.21   $11.20   $11.20  
  7 purchase totals = $672.50       $733.4562   $733.45   $733.45   $733.40