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	$46.37	9.532%	$50.79	$50.79	$50.80	$50.80
Purchase #2	$144.65	4.676%	$151.4138	$151.41	$151.40	$151.40
Purchase #3	$240.79	3.840%	$250.0363	$250.04	$250.05	$250.00
Purchase #4	$167.69	4.526%	$175.2796	$175.28	$175.30	$175.30
Purchase #5	$205.60	8.418%	$222.9074	$222.91	$222.90	$222.90
Purchase #6	$148.80	5.769%	$157.3843	$157.38	$157.40	$157.40
Purchase #7	$101.73	10.792%	$112.7087	$112.71	$112.70	$112.70
7 purchase totals =	$1,055.63		$1,120.5201	$1,120.52	$1,120.55	$1,120.50