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	$17.63	9.259%	$19.2624	$19.26	$19.25	$19.30
Purchase #2	$72.99	13.382%	$82.7575	$82.76	$82.75	$82.80
Purchase #3	$87.47	7.367%	$93.9139	$93.91	$93.90	$93.90
Purchase #4	$145.37	4.716%	$152.2256	$152.23	$152.25	$152.20
Purchase #5	$226.94	12.771%	$255.9225	$255.92	$255.90	$255.90
Purchase #6	$241.73	11.408%	$269.3066	$269.31	$269.30	$269.30
Purchase #7	$40.31	5.438%	$42.5021	$42.50	$42.50	$42.50
7 purchase totals =	$832.44		$915.8906	$915.89	$915.85	$915.90