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	$138.77	6.540%	$147.8456	$147.85	$147.85	$147.80
Purchase #2	$248.31	6.193%	$263.6878	$263.69	$263.70	$263.70
Purchase #3	$197.72	11.482%	$220.4222	$220.42	$220.40	$220.40
Purchase #4	$48.27	13.855%	$54.9578	$54.96	$54.95	$55.00
Purchase #5	$61.85	4.232%	$64.4675	$64.47	$64.45	$64.50
Purchase #6	$150.36	11.510%	$167.6664	$167.67	$167.65	$167.70
Purchase #7	$85.98	3.318%	$88.8328	$88.83	$88.85	$88.80
7 purchase totals =	$931.26		$1,007.8801	$1,007.89	$1,007.85	$1,007.90