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	$119.61	6.536%	$127.4277	$127.43	$127.45	$127.40
Purchase #2	$50.82	7.829%	$54.7987	$54.80	$54.80	$54.80
Purchase #3	$125.59	4.104%	$130.7442	$130.74	$130.75	$130.70
Purchase #4	$206.69	3.464%	$213.8497	$213.85	$213.85	$213.80
Purchase #5	$133.32	13.803%	$151.7222	$151.72	$151.70	$151.70
Purchase #6	$208.50	7.555%	$224.2522	$224.25	$224.25	$224.30
Purchase #7	$27.39	3.634%	$28.3854	$28.39	$28.40	$28.40
7 purchase totals =	$871.92		$931.1801	$931.18	$931.20	$931.10