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 $94.57   8.472%   $102.582   $102.58   $102.60   $102.60  
  Purchase #2 $234.73   4.583%   $245.4877   $245.49   $245.50   $245.50  
  Purchase #3 $58.96   13.352%   $66.8323   $66.83   $66.85   $66.80  
  Purchase #4 $26.83   10.359%   $29.6093   $29.61   $29.60   $29.60  
  Purchase #5 $248.36   9.179%   $271.157   $271.16   $271.15   $271.20  
  Purchase #6 $35.28   7.435%   $37.9031   $37.90   $37.90   $37.90  
  Purchase #7 $122.64   9.286%   $134.0284   $134.03   $134.05   $134.00  
  7 purchase totals = $821.37       $887.5998   $887.60   $887.65   $887.60