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	$35.68	12.713%	$40.216	$40.22	$40.20	$40.20
Purchase #2	$115.77	12.350%	$130.0676	$130.07	$130.05	$130.10
Purchase #3	$54.94	4.264%	$57.2826	$57.28	$57.30	$57.30
Purchase #4	$161.51	6.856%	$172.5831	$172.58	$172.60	$172.60
Purchase #5	$42.86	7.257%	$45.9704	$45.97	$45.95	$46.00
Purchase #6	$96.89	5.692%	$102.405	$102.41	$102.40	$102.40
Purchase #7	$82.79	7.491%	$88.9918	$88.99	$89.00	$89.00
7 purchase totals =	$590.44		$637.5165	$637.52	$637.50	$637.60