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 $73.53   7.718%   $79.205   $79.21   $79.20   $79.20  
  Purchase #2 $45.25   9.581%   $49.5854   $49.59   $49.60   $49.60  
  Purchase #3 $55.42   11.342%   $61.7057   $61.71   $61.70   $61.70  
  Purchase #4 $242.73   9.293%   $265.2869   $265.29   $265.30   $265.30  
  Purchase #5 $179.98   4.655%   $188.3581   $188.36   $188.35   $188.40  
  Purchase #6 $213.43   3.814%   $221.5702   $221.57   $221.55   $221.60  
  Purchase #7 $85.57   11.297%   $95.2368   $95.24   $95.25   $95.20  
  7 purchase totals = $895.91       $960.9481   $960.97   $960.95   $961.00