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 $33.69   13.527%   $38.2472   $38.25   $38.25   $38.20  
  Purchase #2 $217.50   6.218%   $231.0242   $231.02   $231.00   $231.00  
  Purchase #3 $234.26   5.563%   $247.2919   $247.29   $247.30   $247.30  
  Purchase #4 $154.84   5.117%   $162.7632   $162.76   $162.75   $162.80  
  Purchase #5 $206.79   5.660%   $218.4943   $218.49   $218.50   $218.50  
  Purchase #6 $70.52   11.349%   $78.5233   $78.52   $78.50   $78.50  
  Purchase #7 $130.52   3.587%   $135.2018   $135.20   $135.20   $135.20  
  7 purchase totals = $1,048.12       $1,111.5459   $1,111.53   $1,111.50   $1,111.50