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	$150.72	9.675%	$165.3022	$165.30	$165.30	$165.30
Purchase #2	$208.27	6.125%	$221.0265	$221.03	$221.05	$221.00
Purchase #3	$90.58	7.725%	$97.5773	$97.58	$97.60	$97.60
Purchase #4	$188.48	4.175%	$196.349	$196.35	$196.35	$196.30
Purchase #5	$6.62	8.226%	$7.1646	$7.16	$7.15	$7.20
Purchase #6	$158.29	10.139%	$174.339	$174.34	$174.35	$174.30
Purchase #7	$54.82	6.738%	$58.5138	$58.51	$58.50	$58.50
7 purchase totals =	$857.78		$920.2724	$920.27	$920.30	$920.20