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	$120.26	13.108%	$136.0237	$136.02	$136.00	$136.00
Purchase #2	$153.88	11.512%	$171.5947	$171.59	$171.60	$171.60
Purchase #3	$249.98	6.610%	$266.5037	$266.50	$266.50	$266.50
Purchase #4	$228.66	11.674%	$255.3538	$255.35	$255.35	$255.40
Purchase #5	$130.30	5.750%	$137.7923	$137.79	$137.80	$137.80
Purchase #6	$33.40	5.192%	$35.1341	$35.13	$35.15	$35.10
Purchase #7	$36.31	7.240%	$38.9388	$38.94	$38.95	$38.90
7 purchase totals =	$952.79		$1,041.3411	$1,041.32	$1,041.35	$1,041.30