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	$222.87	7.159%	$238.8253	$238.83	$238.85	$238.80
Purchase #2	$182.62	3.750%	$189.4683	$189.47	$189.45	$189.50
Purchase #3	$82.93	11.251%	$92.2605	$92.26	$92.25	$92.30
Purchase #4	$177.82	10.385%	$196.2866	$196.29	$196.30	$196.30
Purchase #5	$30.45	9.536%	$33.3537	$33.35	$33.35	$33.40
Purchase #6	$31.66	11.861%	$35.4152	$35.42	$35.40	$35.40
Purchase #7	$174.59	3.579%	$180.8386	$180.84	$180.85	$180.80
7 purchase totals =	$902.94		$966.4482	$966.46	$966.45	$966.50