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	$105.89	3.639%	$109.7433	$109.74	$109.75	$109.70
Purchase #2	$215.54	9.534%	$236.0896	$236.09	$236.10	$236.10
Purchase #3	$43.79	13.156%	$49.551	$49.55	$49.55	$49.60
Purchase #4	$139.40	4.576%	$145.7789	$145.78	$145.80	$145.80
Purchase #5	$53.43	3.150%	$55.113	$55.11	$55.10	$55.10
Purchase #6	$30.87	5.261%	$32.4941	$32.49	$32.50	$32.50
Purchase #7	$106.56	11.816%	$119.1511	$119.15	$119.15	$119.20
7 purchase totals =	$695.48		$747.9210	$747.91	$747.95	$748.00