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	$249.88	3.515%	$258.6633	$258.66	$258.65	$258.70
Purchase #2	$167.27	3.131%	$172.5072	$172.51	$172.50	$172.50
Purchase #3	$132.41	9.710%	$145.267	$145.27	$145.25	$145.30
Purchase #4	$81.76	9.799%	$89.7717	$89.77	$89.75	$89.80
Purchase #5	$213.25	8.104%	$230.5318	$230.53	$230.55	$230.50
Purchase #6	$104.99	13.564%	$119.2308	$119.23	$119.25	$119.20
Purchase #7	$230.95	10.310%	$254.7609	$254.76	$254.75	$254.80
7 purchase totals =	$1,180.51		$1,270.7327	$1,270.73	$1,270.70	$1,270.80