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 $163.25   12.605%   $183.8277   $183.83   $183.85   $183.80  
  Purchase #2 $44.38   9.634%   $48.6556   $48.66   $48.65   $48.70  
  Purchase #3 $237.47   3.694%   $246.2421   $246.24   $246.25   $246.20  
  Purchase #4 $186.74   5.431%   $196.8818   $196.88   $196.90   $196.90  
  Purchase #5 $242.74   4.714%   $254.1828   $254.18   $254.20   $254.20  
  Purchase #6 $12.84   3.389%   $13.2751   $13.28   $13.30   $13.30  
  Purchase #7 $64.49   13.638%   $73.2851   $73.29   $73.30   $73.30  
  7 purchase totals = $951.91       $1,016.3502   $1,016.36   $1,016.45   $1,016.40