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	$78.25	3.133%	$80.7016	$80.70	$80.70	$80.70
Purchase #2	$134.51	12.464%	$151.2753	$151.28	$151.30	$151.30
Purchase #3	$92.70	6.228%	$98.4734	$98.47	$98.45	$98.50
Purchase #4	$10.61	8.413%	$11.5026	$11.50	$11.50	$11.50
Purchase #5	$235.54	6.567%	$251.0079	$251.01	$251.00	$251.00
Purchase #6	$94.40	6.485%	$100.5218	$100.52	$100.50	$100.50
Purchase #7	$117.27	5.165%	$123.327	$123.33	$123.35	$123.30
7 purchase totals =	$763.28		$816.8096	$816.81	$816.80	$816.80