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 $185.47   6.412%   $197.3623   $197.36   $197.35   $197.40  
  Purchase #2 $65.62   4.604%   $68.6411   $68.64   $68.65   $68.60  
  Purchase #3 $184.26   4.495%   $192.5425   $192.54   $192.55   $192.50  
  Purchase #4 $113.28   3.431%   $117.1666   $117.17   $117.15   $117.20  
  Purchase #5 $151.72   6.658%   $161.8215   $161.82   $161.80   $161.80  
  Purchase #6 $17.67   12.271%   $19.8383   $19.84   $19.85   $19.80  
  Purchase #7 $73.64   4.529%   $76.9752   $76.98   $77.00   $77.00  
  7 purchase totals = $791.66       $834.3475   $834.35   $834.35   $834.30