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	$138.54	9.565%	$151.7914	$151.79	$151.80	$151.80
Purchase #2	$118.37	12.179%	$132.7863	$132.79	$132.80	$132.80
Purchase #3	$195.72	11.780%	$218.7758	$218.78	$218.80	$218.80
Purchase #4	$17.68	9.298%	$19.3239	$19.32	$19.30	$19.30
Purchase #5	$89.25	6.262%	$94.8388	$94.84	$94.85	$94.80
Purchase #6	$14.48	9.215%	$15.8143	$15.81	$15.80	$15.80
Purchase #7	$52.90	12.433%	$59.4771	$59.48	$59.50	$59.50
7 purchase totals =	$626.94		$692.8076	$692.81	$692.85	$692.80