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	$31.77	6.414%	$33.8077	$33.81	$33.80	$33.80
Purchase #2	$79.95	3.864%	$83.0393	$83.04	$83.05	$83.00
Purchase #3	$35.99	5.277%	$37.8892	$37.89	$37.90	$37.90
Purchase #4	$173.40	3.639%	$179.71	$179.71	$179.70	$179.70
Purchase #5	$170.40	10.680%	$188.5987	$188.60	$188.60	$188.60
Purchase #6	$202.29	8.409%	$219.3006	$219.30	$219.30	$219.30
Purchase #7	$89.43	3.223%	$92.3123	$92.31	$92.30	$92.30
7 purchase totals =	$783.23		$834.6578	$834.66	$834.65	$834.60