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	$87.95	13.501%	$99.8241	$99.82	$99.80	$99.80
Purchase #2	$31.87	12.443%	$35.8356	$35.84	$35.85	$35.80
Purchase #3	$241.60	9.316%	$264.1075	$264.11	$264.10	$264.10
Purchase #4	$61.32	11.783%	$68.5453	$68.55	$68.55	$68.50
Purchase #5	$32.63	12.580%	$36.7349	$36.73	$36.75	$36.70
Purchase #6	$71.71	9.613%	$78.6035	$78.60	$78.60	$78.60
Purchase #7	$178.31	10.114%	$196.3443	$196.34	$196.35	$196.30
7 purchase totals =	$705.39		$779.9952	$779.99	$780.00	$779.80