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 $214.86   8.664%   $233.4755   $233.48   $233.50   $233.50  
  Purchase #2 $148.86   7.133%   $159.4782   $159.48   $159.50   $159.50  
  Purchase #3 $53.49   11.147%   $59.4525   $59.45   $59.45   $59.50  
  Purchase #4 $239.67   7.356%   $257.3001   $257.30   $257.30   $257.30  
  Purchase #5 $9.44   13.337%   $10.699   $10.70   $10.70   $10.70  
  Purchase #6 $65.90   3.159%   $67.9818   $67.98   $68.00   $68.00  
  Purchase #7 $195.36   6.450%   $207.9607   $207.96   $207.95   $208.00  
  7 purchase totals = $927.58       $996.3478   $996.35   $996.40   $996.50