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	$223.79	13.380%	$253.7331	$253.73	$253.75	$253.70
Purchase #2	$41.41	5.825%	$43.8221	$43.82	$43.80	$43.80
Purchase #3	$28.73	12.353%	$32.279	$32.28	$32.30	$32.30
Purchase #4	$111.84	11.311%	$124.4902	$124.49	$124.50	$124.50
Purchase #5	$103.36	7.485%	$111.0965	$111.10	$111.10	$111.10
Purchase #6	$119.65	6.596%	$127.5421	$127.54	$127.55	$127.50
Purchase #7	$119.26	13.602%	$135.4817	$135.48	$135.50	$135.50
7 purchase totals =	$748.04		$828.4447	$828.44	$828.50	$828.40