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	$149.84	10.722%	$165.9058	$165.91	$165.90	$165.90
Purchase #2	$123.56	9.195%	$134.9213	$134.92	$134.90	$134.90
Purchase #3	$243.81	4.352%	$254.4206	$254.42	$254.40	$254.40
Purchase #4	$51.42	12.114%	$57.649	$57.65	$57.65	$57.60
Purchase #5	$157.37	6.630%	$167.8036	$167.80	$167.80	$167.80
Purchase #6	$62.86	13.301%	$71.221	$71.22	$71.20	$71.20
Purchase #7	$156.41	7.347%	$167.9014	$167.90	$167.90	$167.90
7 purchase totals =	$945.27		$1,019.8227	$1,019.82	$1,019.75	$1,019.70