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 $66.42   11.169%   $73.8384   $73.84   $73.85   $73.80  
  Purchase #2 $71.84   5.136%   $75.5297   $75.53   $75.55   $75.50  
  Purchase #3 $55.55   4.709%   $58.1658   $58.17   $58.15   $58.20  
  Purchase #4 $86.29   3.699%   $89.4819   $89.48   $89.50   $89.50  
  Purchase #5 $213.28   8.720%   $231.878   $231.88   $231.90   $231.90  
  Purchase #6 $133.90   12.850%   $151.1062   $151.11   $151.10   $151.10  
  Purchase #7 $59.51   10.253%   $65.6116   $65.61   $65.60   $65.60  
  7 purchase totals = $686.79       $745.6116   $745.62   $745.65   $745.60