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	$240.40	3.526%	$248.8765	$248.88	$248.90	$248.90
Purchase #2	$43.34	7.398%	$46.5463	$46.55	$46.55	$46.50
Purchase #3	$84.32	6.768%	$90.0268	$90.03	$90.05	$90.00
Purchase #4	$53.53	11.793%	$59.8428	$59.84	$59.85	$59.80
Purchase #5	$145.51	8.523%	$157.9118	$157.91	$157.90	$157.90
Purchase #6	$20.35	5.342%	$21.4371	$21.44	$21.45	$21.40
Purchase #7	$133.44	9.199%	$145.7151	$145.72	$145.70	$145.70
7 purchase totals =	$720.89		$770.3564	$770.37	$770.40	$770.20