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 $224.59   10.268%   $247.6509   $247.65   $247.65   $247.70  
  Purchase #2 $61.80   8.305%   $66.9325   $66.93   $66.95   $66.90  
  Purchase #3 $129.50   6.495%   $137.911   $137.91   $137.90   $137.90  
  Purchase #4 $89.97   10.109%   $99.0651   $99.07   $99.05   $99.10  
  Purchase #5 $143.54   6.309%   $152.5959   $152.60   $152.60   $152.60  
  Purchase #6 $67.50   12.321%   $75.8167   $75.82   $75.80   $75.80  
  Purchase #7 $189.72   13.684%   $215.6813   $215.68   $215.70   $215.70  
  7 purchase totals = $906.62       $995.6534   $995.66   $995.65   $995.70