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 $231.33   9.621%   $253.5863   $253.59   $253.60   $253.60  
  Purchase #2 $71.47   8.587%   $77.6071   $77.61   $77.60   $77.60  
  Purchase #3 $212.27   7.794%   $228.8143   $228.81   $228.80   $228.80  
  Purchase #4 $57.62   8.669%   $62.6151   $62.62   $62.60   $62.60  
  Purchase #5 $49.85   8.588%   $54.1311   $54.13   $54.15   $54.10  
  Purchase #6 $247.92   4.254%   $258.4665   $258.47   $258.45   $258.50  
  Purchase #7 $72.51   7.355%   $77.8431   $77.84   $77.85   $77.80  
  7 purchase totals = $942.97       $1,013.0635   $1,013.07   $1,013.05   $1,013.00