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	$18.58	10.842%	$20.5944	$20.59	$20.60	$20.60
Purchase #2	$34.80	10.668%	$38.5125	$38.51	$38.50	$38.50
Purchase #3	$41.41	4.674%	$43.3455	$43.35	$43.35	$43.30
Purchase #4	$220.37	11.499%	$245.7103	$245.71	$245.70	$245.70
Purchase #5	$86.81	6.443%	$92.4032	$92.40	$92.40	$92.40
Purchase #6	$103.73	5.525%	$109.4611	$109.46	$109.45	$109.50
Purchase #7	$102.55	5.194%	$107.8764	$107.88	$107.90	$107.90
7 purchase totals =	$608.25		$657.9034	$657.90	$657.90	$657.90