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	$19.33	6.416%	$20.5702	$20.57	$20.55	$20.60
Purchase #2	$213.81	5.801%	$226.2131	$226.21	$226.20	$226.20
Purchase #3	$83.62	13.689%	$95.0667	$95.07	$95.05	$95.10
Purchase #4	$122.95	3.403%	$127.134	$127.13	$127.15	$127.10
Purchase #5	$87.53	3.276%	$90.3975	$90.40	$90.40	$90.40
Purchase #6	$137.66	8.440%	$149.2785	$149.28	$149.30	$149.30
Purchase #7	$85.48	5.635%	$90.2968	$90.30	$90.30	$90.30
7 purchase totals =	$750.38		$798.9568	$798.96	$798.95	$799.00