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	$232.81	4.187%	$242.5578	$242.56	$242.55	$242.60
Purchase #2	$159.32	10.335%	$175.7857	$175.79	$175.80	$175.80
Purchase #3	$106.80	12.218%	$119.8488	$119.85	$119.85	$119.80
Purchase #4	$122.64	7.539%	$131.8858	$131.89	$131.90	$131.90
Purchase #5	$90.92	6.223%	$96.578	$96.58	$96.60	$96.60
Purchase #6	$190.52	4.140%	$198.4075	$198.41	$198.40	$198.40
Purchase #7	$242.82	4.318%	$253.305	$253.31	$253.30	$253.30
7 purchase totals =	$1,145.83		$1,218.3686	$1,218.39	$1,218.40	$1,218.40