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	$148.93	7.108%	$159.5159	$159.52	$159.50	$159.50
Purchase #2	$78.26	6.172%	$83.0902	$83.09	$83.10	$83.10
Purchase #3	$102.58	7.522%	$110.2961	$110.30	$110.30	$110.30
Purchase #4	$129.88	4.722%	$136.0129	$136.01	$136.00	$136.00
Purchase #5	$133.80	10.353%	$147.6523	$147.65	$147.65	$147.70
Purchase #6	$104.78	4.457%	$109.45	$109.45	$109.45	$109.50
Purchase #7	$71.91	9.206%	$78.53	$78.53	$78.55	$78.50
7 purchase totals =	$770.14		$824.5474	$824.55	$824.55	$824.60