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 $171.27   6.827%   $182.9626   $182.96   $182.95   $183.00  
  Purchase #2 $171.42   11.820%   $191.6818   $191.68   $191.70   $191.70  
  Purchase #3 $55.29   9.266%   $60.4132   $60.41   $60.40   $60.40  
  Purchase #4 $38.25   13.630%   $43.4635   $43.46   $43.45   $43.50  
  Purchase #5 $178.76   8.256%   $193.5184   $193.52   $193.50   $193.50  
  Purchase #6 $8.88   8.577%   $9.6416   $9.64   $9.65   $9.60  
  Purchase #7 $132.26   9.516%   $144.8459   $144.85   $144.85   $144.80  
  7 purchase totals = $756.13       $826.5270   $826.52   $826.50   $826.50