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	$112.49	13.118%	$127.2464	$127.25	$127.25	$127.20
Purchase #2	$141.43	12.751%	$159.4637	$159.46	$159.45	$159.50
Purchase #3	$81.90	10.204%	$90.2571	$90.26	$90.25	$90.30
Purchase #4	$102.70	9.289%	$112.2398	$112.24	$112.25	$112.20
Purchase #5	$16.75	13.280%	$18.9744	$18.97	$18.95	$19.00
Purchase #6	$180.52	8.387%	$195.6602	$195.66	$195.65	$195.70
Purchase #7	$57.25	13.835%	$65.1705	$65.17	$65.15	$65.20
7 purchase totals =	$693.04		$769.0121	$769.01	$768.95	$769.10