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	$139.52	6.278%	$148.2791	$148.28	$148.30	$148.30
Purchase #2	$81.87	11.790%	$91.5225	$91.52	$91.50	$91.50
Purchase #3	$130.31	7.726%	$140.3778	$140.38	$140.40	$140.40
Purchase #4	$13.80	3.153%	$14.2351	$14.24	$14.25	$14.20
Purchase #5	$170.40	3.820%	$176.9093	$176.91	$176.90	$176.90
Purchase #6	$103.89	7.727%	$111.9176	$111.92	$111.90	$111.90
Purchase #7	$185.30	5.401%	$195.3081	$195.31	$195.30	$195.30
7 purchase totals =	$825.09		$878.5495	$878.56	$878.55	$878.50