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	$139.46	5.707%	$147.419	$147.42	$147.40	$147.40
Purchase #2	$80.35	11.812%	$89.8409	$89.84	$89.85	$89.80
Purchase #3	$6.90	13.515%	$7.8325	$7.83	$7.85	$7.80
Purchase #4	$28.42	6.717%	$30.329	$30.33	$30.35	$30.30
Purchase #5	$10.86	10.365%	$11.9856	$11.99	$12.00	$12.00
Purchase #6	$128.64	10.687%	$142.3878	$142.39	$142.40	$142.40
Purchase #7	$131.45	4.516%	$137.3863	$137.39	$137.40	$137.40
7 purchase totals =	$526.08		$567.1811	$567.19	$567.25	$567.10