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 $232.64   12.508%   $261.7386   $261.74   $261.75   $261.70  
  Purchase #2 $135.49   7.784%   $146.0365   $146.04   $146.05   $146.00  
  Purchase #3 $79.80   3.799%   $82.8316   $82.83   $82.85   $82.80  
  Purchase #4 $166.78   3.542%   $172.6873   $172.69   $172.70   $172.70  
  Purchase #5 $236.67   4.154%   $246.5013   $246.50   $246.50   $246.50  
  Purchase #6 $250.77   5.793%   $265.2971   $265.30   $265.30   $265.30  
  Purchase #7 $62.52   12.344%   $70.2375   $70.24   $70.25   $70.20  
  7 purchase totals = $1,164.67       $1,245.3299   $1,245.34   $1,245.40   $1,245.20