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 $67.40   13.345%   $76.3945   $76.39   $76.40   $76.40  
  Purchase #2 $228.51   6.167%   $242.6022   $242.60   $242.60   $242.60  
  Purchase #3 $120.98   10.687%   $133.9091   $133.91   $133.90   $133.90  
  Purchase #4 $168.47   13.702%   $191.5538   $191.55   $191.55   $191.60  
  Purchase #5 $36.81   5.727%   $38.9181   $38.92   $38.90   $38.90  
  Purchase #6 $143.63   13.854%   $163.5285   $163.53   $163.55   $163.50  
  Purchase #7 $227.88   11.832%   $254.8428   $254.84   $254.85   $254.80  
  7 purchase totals = $993.68       $1,101.7490   $1,101.74   $1,101.75   $1,101.70