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	$67.60	5.874%	$71.5708	$71.57	$71.55	$71.60
Purchase #2	$223.83	4.739%	$234.4373	$234.44	$234.45	$234.40
Purchase #3	$153.71	6.788%	$164.1438	$164.14	$164.15	$164.10
Purchase #4	$219.43	3.354%	$226.7897	$226.79	$226.80	$226.80
Purchase #5	$190.47	3.544%	$197.2203	$197.22	$197.20	$197.20
Purchase #6	$79.42	12.273%	$89.1672	$89.17	$89.15	$89.20
Purchase #7	$95.27	10.346%	$105.1266	$105.13	$105.15	$105.10
7 purchase totals =	$1,029.73		$1,088.4557	$1,088.46	$1,088.45	$1,088.40