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	$115.34	3.830%	$119.7575	$119.76	$119.75	$119.80
Purchase #2	$148.77	3.708%	$154.2864	$154.29	$154.30	$154.30
Purchase #3	$211.66	5.501%	$223.3034	$223.30	$223.30	$223.30
Purchase #4	$91.69	8.566%	$99.5442	$99.54	$99.55	$99.50
Purchase #5	$173.34	13.320%	$196.4289	$196.43	$196.45	$196.40
Purchase #6	$77.45	4.202%	$80.7044	$80.70	$80.70	$80.70
Purchase #7	$162.45	4.865%	$170.3532	$170.35	$170.35	$170.40
7 purchase totals =	$980.70		$1,044.3780	$1,044.37	$1,044.40	$1,044.40