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	$152.53	3.840%	$158.3872	$158.39	$158.40	$158.40
Purchase #2	$77.58	9.585%	$85.016	$85.02	$85.00	$85.00
Purchase #3	$108.43	6.343%	$115.3077	$115.31	$115.30	$115.30
Purchase #4	$152.41	12.763%	$171.8621	$171.86	$171.85	$171.90
Purchase #5	$119.26	7.261%	$127.9195	$127.92	$127.90	$127.90
Purchase #6	$209.83	4.413%	$219.0898	$219.09	$219.10	$219.10
Purchase #7	$197.58	5.774%	$208.9883	$208.99	$209.00	$209.00
7 purchase totals =	$1,017.62		$1,086.5706	$1,086.58	$1,086.55	$1,086.60