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	$18.55	12.517%	$20.8719	$20.87	$20.85	$20.90
Purchase #2	$212.90	7.313%	$228.4694	$228.47	$228.45	$228.50
Purchase #3	$65.63	3.138%	$67.6895	$67.69	$67.70	$67.70
Purchase #4	$94.70	9.158%	$103.3726	$103.37	$103.35	$103.40
Purchase #5	$216.57	4.348%	$225.9865	$225.99	$226.00	$226.00
Purchase #6	$50.61	9.317%	$55.3253	$55.33	$55.35	$55.30
Purchase #7	$237.41	7.470%	$255.1445	$255.14	$255.15	$255.10
7 purchase totals =	$896.37		$956.8597	$956.86	$956.85	$956.90