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	$150.78	9.837%	$165.6122	$165.61	$165.60	$165.60
Purchase #2	$63.93	6.120%	$67.8425	$67.84	$67.85	$67.80
Purchase #3	$173.62	6.780%	$185.3914	$185.39	$185.40	$185.40
Purchase #4	$46.54	9.244%	$50.8422	$50.84	$50.85	$50.80
Purchase #5	$101.36	12.737%	$114.2702	$114.27	$114.25	$114.30
Purchase #6	$238.45	7.846%	$257.1588	$257.16	$257.15	$257.20
Purchase #7	$90.70	3.830%	$94.1738	$94.17	$94.15	$94.20
7 purchase totals =	$865.38		$935.2911	$935.28	$935.25	$935.30