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	$232.33	13.765%	$264.3102	$264.31	$264.30	$264.30
Purchase #2	$83.82	10.810%	$92.8809	$92.88	$92.90	$92.90
Purchase #3	$35.84	3.664%	$37.1532	$37.15	$37.15	$37.20
Purchase #4	$146.26	3.696%	$151.6658	$151.67	$151.65	$151.70
Purchase #5	$49.45	8.399%	$53.6033	$53.60	$53.60	$53.60
Purchase #6	$120.94	8.601%	$131.342	$131.34	$131.35	$131.30
Purchase #7	$167.94	3.547%	$173.8968	$173.90	$173.90	$173.90
7 purchase totals =	$836.58		$904.8522	$904.85	$904.85	$904.90