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	$121.55	12.148%	$136.3159	$136.32	$136.30	$136.30
Purchase #2	$82.58	8.866%	$89.9015	$89.90	$89.90	$89.90
Purchase #3	$20.71	6.588%	$22.0744	$22.07	$22.05	$22.10
Purchase #4	$118.27	9.414%	$129.4039	$129.40	$129.40	$129.40
Purchase #5	$93.96	5.539%	$99.1644	$99.16	$99.15	$99.20
Purchase #6	$219.47	4.568%	$229.4954	$229.50	$229.50	$229.50
Purchase #7	$58.84	13.527%	$66.7993	$66.80	$66.80	$66.80
7 purchase totals =	$715.38		$773.1548	$773.15	$773.10	$773.20