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 $196.90   4.788%   $206.3276   $206.33   $206.35   $206.30  
  Purchase #2 $76.64   10.736%   $84.8681   $84.87   $84.85   $84.90  
  Purchase #3 $97.52   12.428%   $109.6398   $109.64   $109.65   $109.60  
  Purchase #4 $238.81   10.103%   $262.937   $262.94   $262.95   $262.90  
  Purchase #5 $98.95   9.531%   $108.3809   $108.38   $108.40   $108.40  
  Purchase #6 $161.48   4.508%   $168.7595   $168.76   $168.75   $168.80  
  Purchase #7 $68.29   11.246%   $75.9699   $75.97   $75.95   $76.00  
  7 purchase totals = $938.59       $1,016.8828   $1,016.89   $1,016.90   $1,016.90