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	$137.32	6.732%	$146.5644	$146.56	$146.55	$146.60
Purchase #2	$81.80	12.833%	$92.2974	$92.30	$92.30	$92.30
Purchase #3	$236.35	12.823%	$266.6572	$266.66	$266.65	$266.70
Purchase #4	$171.89	7.268%	$184.383	$184.38	$184.40	$184.40
Purchase #5	$35.87	4.756%	$37.576	$37.58	$37.60	$37.60
Purchase #6	$188.72	13.355%	$213.9236	$213.92	$213.90	$213.90
Purchase #7	$75.30	9.855%	$82.7208	$82.72	$82.70	$82.70
7 purchase totals =	$927.25		$1,024.1224	$1,024.12	$1,024.10	$1,024.20