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 $66.98   12.789%   $75.5461   $75.55   $75.55   $75.50  
  Purchase #2 $134.93   4.860%   $141.4876   $141.49   $141.50   $141.50  
  Purchase #3 $153.59   11.222%   $170.8259   $170.83   $170.85   $170.80  
  Purchase #4 $249.74   3.466%   $258.396   $258.40   $258.40   $258.40  
  Purchase #5 $60.96   3.634%   $63.1753   $63.18   $63.20   $63.20  
  Purchase #6 $44.98   7.141%   $48.192   $48.19   $48.20   $48.20  
  Purchase #7 $44.93   5.856%   $47.5611   $47.56   $47.55   $47.60  
  7 purchase totals = $756.11       $805.1840   $805.20   $805.25   $805.20