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 $148.49   7.249%   $159.254   $159.25   $159.25   $159.30  
  Purchase #2 $63.83   4.299%   $66.5741   $66.57   $66.55   $66.60  
  Purchase #3 $48.49   6.267%   $51.5289   $51.53   $51.55   $51.50  
  Purchase #4 $233.62   5.562%   $246.6139   $246.61   $246.60   $246.60  
  Purchase #5 $20.63   11.179%   $22.9362   $22.94   $22.95   $22.90  
  Purchase #6 $136.70   5.519%   $144.2445   $144.24   $144.25   $144.20  
  Purchase #7 $79.25   6.549%   $84.4401   $84.44   $84.45   $84.40  
  7 purchase totals = $731.01       $775.5917   $775.58   $775.60   $775.50