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	$24.28	4.414%	$25.3517	$25.35	$25.35	$25.40
Purchase #2	$146.88	13.379%	$166.5311	$166.53	$166.55	$166.50
Purchase #3	$153.52	7.113%	$164.4399	$164.44	$164.45	$164.40
Purchase #4	$46.55	11.724%	$52.0075	$52.01	$52.00	$52.00
Purchase #5	$77.62	6.364%	$82.5597	$82.56	$82.55	$82.60
Purchase #6	$186.27	3.512%	$192.8118	$192.81	$192.80	$192.80
Purchase #7	$150.34	10.667%	$166.3768	$166.38	$166.40	$166.40
7 purchase totals =	$785.46		$850.0785	$850.08	$850.10	$850.10