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	$240.61	3.411%	$248.8172	$248.82	$248.80	$248.80
Purchase #2	$34.36	10.356%	$37.9183	$37.92	$37.90	$37.90
Purchase #3	$64.71	5.841%	$68.4897	$68.49	$68.50	$68.50
Purchase #4	$47.76	7.124%	$51.1624	$51.16	$51.15	$51.20
Purchase #5	$56.96	7.514%	$61.24	$61.24	$61.25	$61.20
Purchase #6	$127.92	10.464%	$141.3055	$141.31	$141.30	$141.30
Purchase #7	$50.47	4.401%	$52.6912	$52.69	$52.70	$52.70
7 purchase totals =	$622.79		$661.6243	$661.63	$661.60	$661.60