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	$245.74	11.279%	$273.457	$273.46	$273.45	$273.50
Purchase #2	$38.82	10.433%	$42.8701	$42.87	$42.85	$42.90
Purchase #3	$133.39	3.111%	$137.5398	$137.54	$137.55	$137.50
Purchase #4	$16.31	12.132%	$18.2887	$18.29	$18.30	$18.30
Purchase #5	$128.84	13.619%	$146.3867	$146.39	$146.40	$146.40
Purchase #6	$79.87	10.827%	$88.5175	$88.52	$88.50	$88.50
Purchase #7	$28.28	7.825%	$30.4929	$30.49	$30.50	$30.50
7 purchase totals =	$671.25		$737.5527	$737.56	$737.55	$737.60