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	$96.89	3.379%	$100.1639	$100.16	$100.15	$100.20
Purchase #2	$77.85	13.612%	$88.4469	$88.45	$88.45	$88.40
Purchase #3	$219.41	11.465%	$244.5654	$244.57	$244.55	$244.60
Purchase #4	$17.25	13.413%	$19.5637	$19.56	$19.55	$19.60
Purchase #5	$175.75	8.306%	$190.3478	$190.35	$190.35	$190.30
Purchase #6	$199.89	10.123%	$220.1249	$220.12	$220.10	$220.10
Purchase #7	$148.61	9.268%	$162.3832	$162.38	$162.40	$162.40
7 purchase totals =	$935.65		$1,025.5958	$1,025.59	$1,025.55	$1,025.60