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	$88.62	13.390%	$100.4862	$100.49	$100.50	$100.50
Purchase #2	$174.49	12.546%	$196.3815	$196.38	$196.40	$196.40
Purchase #3	$242.35	3.354%	$250.4784	$250.48	$250.50	$250.50
Purchase #4	$164.38	12.394%	$184.7533	$184.75	$184.75	$184.80
Purchase #5	$77.53	4.512%	$81.0282	$81.03	$81.05	$81.00
Purchase #6	$226.85	13.637%	$257.7855	$257.79	$257.80	$257.80
Purchase #7	$128.30	9.454%	$140.4295	$140.43	$140.45	$140.40
7 purchase totals =	$1,102.52		$1,211.3426	$1,211.35	$1,211.45	$1,211.40