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	$171.33	10.138%	$188.6994	$188.70	$188.70	$188.70
Purchase #2	$114.25	11.871%	$127.8126	$127.81	$127.80	$127.80
Purchase #3	$97.93	9.683%	$107.4126	$107.41	$107.40	$107.40
Purchase #4	$11.98	13.630%	$13.6129	$13.61	$13.60	$13.60
Purchase #5	$101.65	7.501%	$109.2748	$109.27	$109.25	$109.30
Purchase #6	$94.95	3.352%	$98.1327	$98.13	$98.15	$98.10
Purchase #7	$89.32	10.591%	$98.7799	$98.78	$98.80	$98.80
7 purchase totals =	$681.41		$743.7249	$743.71	$743.70	$743.70