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	$235.48	3.447%	$243.597	$243.60	$243.60	$243.60
Purchase #2	$171.43	6.118%	$181.9181	$181.92	$181.90	$181.90
Purchase #3	$60.79	6.236%	$64.5809	$64.58	$64.60	$64.60
Purchase #4	$79.74	3.484%	$82.5181	$82.52	$82.50	$82.50
Purchase #5	$70.86	3.735%	$73.5066	$73.51	$73.50	$73.50
Purchase #6	$52.62	10.660%	$58.2293	$58.23	$58.25	$58.20
Purchase #7	$101.37	8.117%	$109.5982	$109.60	$109.60	$109.60
7 purchase totals =	$772.29		$813.9482	$813.96	$813.95	$813.90