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	$230.85	11.837%	$258.1757	$258.18	$258.20	$258.20
Purchase #2	$162.89	13.641%	$185.1098	$185.11	$185.10	$185.10
Purchase #3	$65.82	6.784%	$70.2852	$70.29	$70.30	$70.30
Purchase #4	$32.66	13.678%	$37.1272	$37.13	$37.15	$37.10
Purchase #5	$59.66	3.349%	$61.658	$61.66	$61.65	$61.70
Purchase #6	$39.44	6.244%	$41.9026	$41.90	$41.90	$41.90
Purchase #7	$239.81	3.471%	$248.1338	$248.13	$248.15	$248.10
7 purchase totals =	$831.13		$902.3923	$902.40	$902.45	$902.40