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	$78.67	8.126%	$85.0627	$85.06	$85.05	$85.10
Purchase #2	$29.30	4.614%	$30.6519	$30.65	$30.65	$30.70
Purchase #3	$92.78	9.467%	$101.5635	$101.56	$101.55	$101.60
Purchase #4	$52.63	9.400%	$57.5772	$57.58	$57.60	$57.60
Purchase #5	$99.74	11.780%	$111.4894	$111.49	$111.50	$111.50
Purchase #6	$170.95	7.163%	$183.1951	$183.20	$183.20	$183.20
Purchase #7	$102.76	6.570%	$109.5113	$109.51	$109.50	$109.50
7 purchase totals =	$626.83		$679.0511	$679.05	$679.05	$679.20