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	$100.42	4.207%	$104.6447	$104.64	$104.65	$104.60
Purchase #2	$43.70	9.506%	$47.8541	$47.85	$47.85	$47.90
Purchase #3	$105.76	3.666%	$109.6372	$109.64	$109.65	$109.60
Purchase #4	$74.54	5.284%	$78.4787	$78.48	$78.50	$78.50
Purchase #5	$108.93	8.483%	$118.1705	$118.17	$118.15	$118.20
Purchase #6	$104.84	7.339%	$112.5342	$112.53	$112.55	$112.50
Purchase #7	$232.74	8.152%	$251.713	$251.71	$251.70	$251.70
7 purchase totals =	$770.93		$823.0324	$823.02	$823.05	$823.00