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 $238.51   9.242%   $260.5531   $260.55   $260.55   $260.60  
  Purchase #2 $179.37   12.781%   $202.2953   $202.30   $202.30   $202.30  
  Purchase #3 $50.33   11.707%   $56.2221   $56.22   $56.20   $56.20  
  Purchase #4 $215.45   5.719%   $227.7716   $227.77   $227.75   $227.80  
  Purchase #5 $72.86   12.660%   $82.0841   $82.08   $82.10   $82.10  
  Purchase #6 $178.28   9.802%   $195.755   $195.76   $195.75   $195.80  
  Purchase #7 $57.25   5.845%   $60.5963   $60.60   $60.60   $60.60  
  7 purchase totals = $992.05       $1,085.2775   $1,085.28   $1,085.25   $1,085.40