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	$5.62	11.754%	$6.2806	$6.28	$6.30	$6.30
Purchase #2	$32.73	11.567%	$36.5159	$36.52	$36.50	$36.50
Purchase #3	$186.89	12.467%	$210.1896	$210.19	$210.20	$210.20
Purchase #4	$49.72	13.609%	$56.4864	$56.49	$56.50	$56.50
Purchase #5	$101.53	7.529%	$109.1742	$109.17	$109.15	$109.20
Purchase #6	$133.32	6.141%	$141.5072	$141.51	$141.50	$141.50
Purchase #7	$144.82	12.334%	$162.6821	$162.68	$162.70	$162.70
7 purchase totals =	$654.63		$722.8360	$722.84	$722.85	$722.90