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 $219.94   11.260%   $244.7052   $244.71   $244.70   $244.70  
  Purchase #2 $207.78   5.790%   $219.8105   $219.81   $219.80   $219.80  
  Purchase #3 $160.44   3.753%   $166.4613   $166.46   $166.45   $166.50  
  Purchase #4 $64.94   6.173%   $68.9487   $68.95   $68.95   $68.90  
  Purchase #5 $248.37   5.388%   $261.7522   $261.75   $261.75   $261.80  
  Purchase #6 $106.66   12.323%   $119.8037   $119.80   $119.80   $119.80  
  Purchase #7 $144.70   3.496%   $149.7587   $149.76   $149.75   $149.80  
  7 purchase totals = $1,152.83       $1,231.2403   $1,231.24   $1,231.20   $1,231.30