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 $103.78   10.812%   $115.0007   $115.00   $115.00   $115.00  
  Purchase #2 $31.48   13.436%   $35.7097   $35.71   $35.70   $35.70  
  Purchase #3 $141.39   8.468%   $153.3629   $153.36   $153.35   $153.40  
  Purchase #4 $63.71   8.294%   $68.9941   $68.99   $69.00   $69.00  
  Purchase #5 $152.92   6.189%   $162.3842   $162.38   $162.40   $162.40  
  Purchase #6 $216.47   4.628%   $226.4882   $226.49   $226.50   $226.50  
  Purchase #7 $69.28   5.821%   $73.3128   $73.31   $73.30   $73.30  
  7 purchase totals = $779.03       $835.2526   $835.24   $835.25   $835.30