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	$99.37	6.133%	$105.4644	$105.46	$105.45	$105.50
Purchase #2	$40.49	11.860%	$45.2921	$45.29	$45.30	$45.30
Purchase #3	$67.74	5.835%	$71.6926	$71.69	$71.70	$71.70
Purchase #4	$47.61	6.313%	$50.6156	$50.62	$50.60	$50.60
Purchase #5	$170.34	5.658%	$179.9778	$179.98	$180.00	$180.00
Purchase #6	$58.49	5.640%	$61.7888	$61.79	$61.80	$61.80
Purchase #7	$35.80	10.872%	$39.6922	$39.69	$39.70	$39.70
7 purchase totals =	$519.84		$554.5235	$554.52	$554.55	$554.60