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	$240.75	3.375%	$248.8753	$248.88	$248.90	$248.90
Purchase #2	$24.36	13.217%	$27.5797	$27.58	$27.60	$27.60
Purchase #3	$7.55	3.660%	$7.8263	$7.83	$7.85	$7.80
Purchase #4	$47.68	9.773%	$52.3398	$52.34	$52.35	$52.30
Purchase #5	$45.33	12.267%	$50.8906	$50.89	$50.90	$50.90
Purchase #6	$204.76	3.137%	$211.1833	$211.18	$211.20	$211.20
Purchase #7	$148.83	11.265%	$165.5957	$165.60	$165.60	$165.60
7 purchase totals =	$719.26		$764.2907	$764.30	$764.40	$764.30