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	$249.68	4.517%	$260.958	$260.96	$260.95	$261.00
Purchase #2	$214.55	13.826%	$244.2137	$244.21	$244.20	$244.20
Purchase #3	$125.72	4.832%	$131.7948	$131.79	$131.80	$131.80
Purchase #4	$40.75	12.616%	$45.891	$45.89	$45.90	$45.90
Purchase #5	$75.56	13.448%	$85.7213	$85.72	$85.70	$85.70
Purchase #6	$230.26	9.829%	$252.8923	$252.89	$252.90	$252.90
Purchase #7	$150.36	11.810%	$168.1175	$168.12	$168.10	$168.10
7 purchase totals =	$1,086.88		$1,189.5886	$1,189.58	$1,189.55	$1,189.60