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	$144.67	8.766%	$157.3518	$157.35	$157.35	$157.40
Purchase #2	$44.33	12.556%	$49.8961	$49.90	$49.90	$49.90
Purchase #3	$65.98	8.701%	$71.7209	$71.72	$71.70	$71.70
Purchase #4	$49.53	10.277%	$54.6202	$54.62	$54.60	$54.60
Purchase #5	$56.89	6.674%	$60.6868	$60.69	$60.70	$60.70
Purchase #6	$165.48	3.428%	$171.1527	$171.15	$171.15	$171.20
Purchase #7	$99.28	4.502%	$103.7496	$103.75	$103.75	$103.70
7 purchase totals =	$626.16		$669.1781	$669.18	$669.15	$669.20