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 $38.81   10.699%   $42.9623   $42.96   $42.95   $43.00  
  Purchase #2 $244.96   10.785%   $271.3789   $271.38   $271.40   $271.40  
  Purchase #3 $77.42   3.267%   $79.9493   $79.95   $79.95   $79.90  
  Purchase #4 $108.53   10.479%   $119.9029   $119.90   $119.90   $119.90  
  Purchase #5 $155.94   7.492%   $167.623   $167.62   $167.60   $167.60  
  Purchase #6 $61.39   5.562%   $64.8045   $64.80   $64.80   $64.80  
  Purchase #7 $206.64   11.829%   $231.0834   $231.08   $231.10   $231.10  
  7 purchase totals = $893.69       $977.7043   $977.69   $977.70   $977.70