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 $239.76   12.148%   $268.886   $268.89   $268.90   $268.90  
  Purchase #2 $98.47   3.308%   $101.7274   $101.73   $101.75   $101.70  
  Purchase #3 $65.50   6.864%   $69.9959   $70.00   $70.00   $70.00  
  Purchase #4 $159.86   12.568%   $179.9512   $179.95   $179.95   $180.00  
  Purchase #5 $100.45   4.369%   $104.8387   $104.84   $104.85   $104.80  
  Purchase #6 $66.86   12.420%   $75.164   $75.16   $75.15   $75.20  
  Purchase #7 $155.69   11.110%   $172.9872   $172.99   $173.00   $173.00  
  7 purchase totals = $886.59       $973.5504   $973.56   $973.60   $973.60