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	$48.61	10.862%	$53.89	$53.89	$53.90	$53.90
Purchase #2	$153.64	10.740%	$170.1409	$170.14	$170.15	$170.10
Purchase #3	$54.62	9.461%	$59.7876	$59.79	$59.80	$59.80
Purchase #4	$135.90	4.183%	$141.5847	$141.58	$141.60	$141.60
Purchase #5	$99.97	12.433%	$112.3993	$112.40	$112.40	$112.40
Purchase #6	$34.35	10.448%	$37.9389	$37.94	$37.95	$37.90
Purchase #7	$97.77	13.464%	$110.9338	$110.93	$110.95	$110.90
7 purchase totals =	$624.86		$686.6752	$686.67	$686.75	$686.60