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	$20.44	9.841%	$22.4515	$22.45	$22.45	$22.50
Purchase #2	$59.34	12.793%	$66.9314	$66.93	$66.95	$66.90
Purchase #3	$63.51	6.337%	$67.5346	$67.53	$67.55	$67.50
Purchase #4	$36.72	6.417%	$39.0763	$39.08	$39.10	$39.10
Purchase #5	$226.73	5.858%	$240.0118	$240.01	$240.00	$240.00
Purchase #6	$198.56	12.620%	$223.6183	$223.62	$223.60	$223.60
Purchase #7	$76.99	6.715%	$82.1599	$82.16	$82.15	$82.20
7 purchase totals =	$682.29		$741.7838	$741.78	$741.80	$741.80