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 $117.97   4.691%   $123.504   $123.50   $123.50   $123.50  
  Purchase #2 $192.41   7.556%   $206.9485   $206.95   $206.95   $206.90  
  Purchase #3 $159.95   11.196%   $177.858   $177.86   $177.85   $177.90  
  Purchase #4 $40.56   6.712%   $43.2824   $43.28   $43.30   $43.30  
  Purchase #5 $95.72   9.378%   $104.6966   $104.70   $104.70   $104.70  
  Purchase #6 $169.80   5.111%   $178.4785   $178.48   $178.50   $178.50  
  Purchase #7 $161.93   8.706%   $176.0276   $176.03   $176.05   $176.00  
  7 purchase totals = $938.34       $1,010.7956   $1,010.80   $1,010.85   $1,010.80