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	$17.90	13.693%	$20.351	$20.35	$20.35	$20.40
Purchase #2	$156.73	10.702%	$173.5032	$173.50	$173.50	$173.50
Purchase #3	$202.30	11.398%	$225.3582	$225.36	$225.35	$225.40
Purchase #4	$45.52	10.785%	$50.4293	$50.43	$50.45	$50.40
Purchase #5	$134.80	4.677%	$141.1046	$141.10	$141.10	$141.10
Purchase #6	$121.73	8.118%	$131.612	$131.61	$131.60	$131.60
Purchase #7	$201.46	11.734%	$225.0993	$225.10	$225.10	$225.10
7 purchase totals =	$880.44		$967.4576	$967.45	$967.45	$967.50