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 $87.81   5.602%   $92.7291   $92.73   $92.75   $92.70  
  Purchase #2 $184.57   9.662%   $202.4032   $202.40   $202.40   $202.40  
  Purchase #3 $133.46   6.279%   $141.84   $141.84   $141.85   $141.80  
  Purchase #4 $243.29   9.734%   $266.9718   $266.97   $266.95   $267.00  
  Purchase #5 $184.88   6.835%   $197.5165   $197.52   $197.50   $197.50  
  Purchase #6 $117.42   13.162%   $132.8748   $132.87   $132.85   $132.90  
  Purchase #7 $91.93   10.788%   $101.8474   $101.85   $101.85   $101.80  
  7 purchase totals = $1,043.36       $1,136.1828   $1,136.18   $1,136.15   $1,136.10