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 $248.83   5.198%   $261.7642   $261.76   $261.75   $261.80  
  Purchase #2 $235.35   13.521%   $267.1717   $267.17   $267.15   $267.20  
  Purchase #3 $248.46   4.321%   $259.196   $259.20   $259.20   $259.20  
  Purchase #4 $62.83   10.301%   $69.3021   $69.30   $69.30   $69.30  
  Purchase #5 $157.85   5.533%   $166.5838   $166.58   $166.60   $166.60  
  Purchase #6 $231.25   4.440%   $241.5175   $241.52   $241.50   $241.50  
  Purchase #7 $10.70   8.806%   $11.6422   $11.64   $11.65   $11.60  
  7 purchase totals = $1,195.27       $1,277.1775   $1,277.17   $1,277.15   $1,277.20