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	$120.42	12.834%	$135.8747	$135.87	$135.85	$135.90
Purchase #2	$18.79	9.857%	$20.6421	$20.64	$20.65	$20.60
Purchase #3	$94.27	6.323%	$100.2307	$100.23	$100.25	$100.20
Purchase #4	$141.76	7.323%	$152.1411	$152.14	$152.15	$152.10
Purchase #5	$62.70	10.304%	$69.1606	$69.16	$69.15	$69.20
Purchase #6	$102.75	6.389%	$109.3147	$109.31	$109.30	$109.30
Purchase #7	$249.77	4.287%	$260.4776	$260.48	$260.50	$260.50
7 purchase totals =	$790.46		$847.8415	$847.83	$847.85	$847.80