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 $70.65   3.546%   $73.1552   $73.16   $73.15   $73.20  
  Purchase #2 $101.73   11.532%   $113.4615   $113.46   $113.45   $113.50  
  Purchase #3 $244.67   9.848%   $268.7651   $268.77   $268.75   $268.80  
  Purchase #4 $89.48   7.380%   $96.0836   $96.08   $96.10   $96.10  
  Purchase #5 $197.83   6.665%   $211.0154   $211.02   $211.00   $211.00  
  Purchase #6 $123.64   9.606%   $135.5169   $135.52   $135.50   $135.50  
  Purchase #7 $124.80   10.802%   $138.2809   $138.28   $138.30   $138.30  
  7 purchase totals = $952.80       $1,036.2786   $1,036.29   $1,036.25   $1,036.40