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 $73.33   8.148%   $79.3049   $79.30   $79.30   $79.30  
  Purchase #2 $227.84   3.239%   $235.2197   $235.22   $235.20   $235.20  
  Purchase #3 $186.71   4.727%   $195.5358   $195.54   $195.55   $195.50  
  Purchase #4 $89.60   5.783%   $94.7816   $94.78   $94.80   $94.80  
  Purchase #5 $83.25   11.427%   $92.763   $92.76   $92.75   $92.80  
  Purchase #6 $171.39   9.745%   $188.092   $188.09   $188.10   $188.10  
  Purchase #7 $84.66   6.670%   $90.3068   $90.31   $90.30   $90.30  
  7 purchase totals = $916.78       $976.0038   $976.00   $976.00   $976.00