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	$150.53	3.530%	$155.8437	$155.84	$155.85	$155.80
Purchase #2	$105.79	4.384%	$110.4278	$110.43	$110.45	$110.40
Purchase #3	$33.63	5.204%	$35.3801	$35.38	$35.40	$35.40
Purchase #4	$76.45	4.677%	$80.0256	$80.03	$80.05	$80.00
Purchase #5	$119.51	3.274%	$123.4228	$123.42	$123.40	$123.40
Purchase #6	$213.35	6.608%	$227.4482	$227.45	$227.45	$227.40
Purchase #7	$77.47	11.824%	$86.6301	$86.63	$86.65	$86.60
7 purchase totals =	$776.73		$819.1783	$819.18	$819.25	$819.00