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	$72.30	10.414%	$79.8293	$79.83	$79.85	$79.80
Purchase #2	$77.61	3.873%	$80.6158	$80.62	$80.60	$80.60
Purchase #3	$72.53	8.849%	$78.9482	$78.95	$78.95	$78.90
Purchase #4	$123.80	10.300%	$136.5514	$136.55	$136.55	$136.60
Purchase #5	$7.62	12.400%	$8.5649	$8.56	$8.55	$8.60
Purchase #6	$189.63	11.788%	$211.9836	$211.98	$212.00	$212.00
Purchase #7	$34.58	3.699%	$35.8591	$35.86	$35.85	$35.90
7 purchase totals =	$578.07		$632.3523	$632.35	$632.35	$632.40