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 $33.41   4.717%   $34.9859   $34.99   $35.00   $35.00  
  Purchase #2 $15.25   6.837%   $16.2926   $16.29   $16.30   $16.30  
  Purchase #3 $218.71   9.639%   $239.7915   $239.79   $239.80   $239.80  
  Purchase #4 $236.85   12.795%   $267.155   $267.16   $267.15   $267.20  
  Purchase #5 $41.50   7.534%   $44.6266   $44.63   $44.65   $44.60  
  Purchase #6 $105.39   6.723%   $112.4754   $112.48   $112.50   $112.50  
  Purchase #7 $231.47   6.131%   $245.6614   $245.66   $245.65   $245.70  
  7 purchase totals = $882.58       $960.9884   $961.00   $961.05   $961.10