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	$47.30	13.670%	$53.7659	$53.77	$53.75	$53.80
Purchase #2	$155.52	9.113%	$169.6925	$169.69	$169.70	$169.70
Purchase #3	$91.90	10.260%	$101.3289	$101.33	$101.35	$101.30
Purchase #4	$148.89	4.515%	$155.6124	$155.61	$155.60	$155.60
Purchase #5	$88.43	5.605%	$93.3865	$93.39	$93.40	$93.40
Purchase #6	$31.75	12.812%	$35.8178	$35.82	$35.80	$35.80
Purchase #7	$35.38	6.622%	$37.7229	$37.72	$37.70	$37.70
7 purchase totals =	$599.17		$647.3269	$647.33	$647.30	$647.30