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 $10.67   7.590%   $11.4799   $11.48   $11.50   $11.50  
  Purchase #2 $176.64   11.832%   $197.54   $197.54   $197.55   $197.50  
  Purchase #3 $69.39   9.681%   $76.1076   $76.11   $76.10   $76.10  
  Purchase #4 $206.82   3.783%   $214.644   $214.64   $214.65   $214.60  
  Purchase #5 $32.89   6.173%   $34.9203   $34.92   $34.90   $34.90  
  Purchase #6 $117.56   11.616%   $131.2158   $131.22   $131.20   $131.20  
  Purchase #7 $78.96   6.513%   $84.1027   $84.10   $84.10   $84.10  
  7 purchase totals = $692.93       $750.0103   $750.01   $750.00   $749.90