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	$238.56	6.657%	$254.4409	$254.44	$254.45	$254.40
Purchase #2	$50.81	11.287%	$56.5449	$56.54	$56.55	$56.50
Purchase #3	$119.37	7.335%	$128.1258	$128.13	$128.15	$128.10
Purchase #4	$190.92	10.568%	$211.0964	$211.10	$211.10	$211.10
Purchase #5	$118.82	11.607%	$132.6114	$132.61	$132.60	$132.60
Purchase #6	$201.40	7.454%	$216.4124	$216.41	$216.40	$216.40
Purchase #7	$162.25	3.634%	$168.1462	$168.15	$168.15	$168.10
7 purchase totals =	$1,082.13		$1,167.3780	$1,167.38	$1,167.40	$1,167.20