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	$105.62	5.517%	$111.4471	$111.45	$111.45	$111.40
Purchase #2	$215.73	8.862%	$234.848	$234.85	$234.85	$234.80
Purchase #3	$85.31	10.476%	$94.2471	$94.25	$94.25	$94.20
Purchase #4	$65.64	11.844%	$73.4144	$73.41	$73.40	$73.40
Purchase #5	$140.97	4.111%	$146.7653	$146.77	$146.75	$146.80
Purchase #6	$35.80	11.479%	$39.9095	$39.91	$39.90	$39.90
Purchase #7	$37.48	13.726%	$42.6245	$42.62	$42.60	$42.60
7 purchase totals =	$686.55		$743.2559	$743.26	$743.20	$743.10