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	$29.97	3.472%	$31.0106	$31.01	$31.00	$31.00
Purchase #2	$40.54	6.104%	$43.0146	$43.01	$43.00	$43.00
Purchase #3	$18.91	13.512%	$21.4651	$21.47	$21.45	$21.50
Purchase #4	$163.74	10.125%	$180.3187	$180.32	$180.30	$180.30
Purchase #5	$89.83	7.622%	$96.6768	$96.68	$96.70	$96.70
Purchase #6	$159.54	4.292%	$166.3875	$166.39	$166.40	$166.40
Purchase #7	$140.79	10.360%	$155.3758	$155.38	$155.40	$155.40
7 purchase totals =	$643.32		$694.2491	$694.26	$694.25	$694.30