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	$17.58	9.302%	$19.2153	$19.22	$19.20	$19.20
Purchase #2	$82.55	8.178%	$89.3009	$89.30	$89.30	$89.30
Purchase #3	$135.82	10.673%	$150.3161	$150.32	$150.30	$150.30
Purchase #4	$14.67	6.506%	$15.6244	$15.62	$15.60	$15.60
Purchase #5	$182.86	7.569%	$196.7007	$196.70	$196.70	$196.70
Purchase #6	$217.76	6.111%	$231.0673	$231.07	$231.05	$231.10
Purchase #7	$107.93	9.740%	$118.4424	$118.44	$118.45	$118.40
7 purchase totals =	$759.17		$820.6671	$820.67	$820.60	$820.60