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	$37.64	12.406%	$42.3096	$42.31	$42.30	$42.30
Purchase #2	$168.53	4.239%	$175.674	$175.67	$175.65	$175.70
Purchase #3	$156.63	9.529%	$171.5553	$171.56	$171.55	$171.60
Purchase #4	$116.28	13.216%	$131.6476	$131.65	$131.65	$131.60
Purchase #5	$223.80	7.464%	$240.5044	$240.50	$240.50	$240.50
Purchase #6	$176.87	6.619%	$188.577	$188.58	$188.60	$188.60
Purchase #7	$212.65	10.728%	$235.4631	$235.46	$235.45	$235.50
7 purchase totals =	$1,092.40		$1,185.7310	$1,185.73	$1,185.70	$1,185.80