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 $117.69   12.826%   $132.7849   $132.78   $132.80   $132.80  
  Purchase #2 $97.54   4.170%   $101.6074   $101.61   $101.60   $101.60  
  Purchase #3 $242.85   10.739%   $268.9297   $268.93   $268.95   $268.90  
  Purchase #4 $225.77   8.277%   $244.457   $244.46   $244.45   $244.50  
  Purchase #5 $209.54   3.446%   $216.7607   $216.76   $216.75   $216.80  
  Purchase #6 $73.87   3.591%   $76.5227   $76.52   $76.50   $76.50  
  Purchase #7 $160.33   7.723%   $172.7123   $172.71   $172.70   $172.70  
  7 purchase totals = $1,127.59       $1,213.7747   $1,213.77   $1,213.75   $1,213.80