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	$53.53	12.716%	$60.3369	$60.34	$60.35	$60.30
Purchase #2	$78.46	5.335%	$82.6458	$82.65	$82.65	$82.60
Purchase #3	$35.53	10.477%	$39.2525	$39.25	$39.25	$39.30
Purchase #4	$191.42	3.760%	$198.6174	$198.62	$198.60	$198.60
Purchase #5	$60.48	10.804%	$67.0143	$67.01	$67.00	$67.00
Purchase #6	$91.28	8.764%	$99.2798	$99.28	$99.30	$99.30
Purchase #7	$43.48	4.867%	$45.5962	$45.60	$45.60	$45.60
7 purchase totals =	$554.18		$592.7429	$592.75	$592.75	$592.70