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	$79.73	10.768%	$88.3153	$88.32	$88.30	$88.30
Purchase #2	$73.50	6.721%	$78.4399	$78.44	$78.45	$78.40
Purchase #3	$136.35	4.200%	$142.0767	$142.08	$142.10	$142.10
Purchase #4	$149.35	7.520%	$160.5811	$160.58	$160.60	$160.60
Purchase #5	$105.39	3.849%	$109.4465	$109.45	$109.45	$109.40
Purchase #6	$99.95	12.331%	$112.2748	$112.27	$112.25	$112.30
Purchase #7	$141.91	9.685%	$155.654	$155.65	$155.65	$155.70
7 purchase totals =	$786.18		$846.7883	$846.79	$846.80	$846.80