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	$20.27	4.384%	$21.1586	$21.16	$21.15	$21.20
Purchase #2	$44.61	11.614%	$49.791	$49.79	$49.80	$49.80
Purchase #3	$38.70	13.696%	$44.0004	$44.00	$44.00	$44.00
Purchase #4	$100.96	10.658%	$111.7203	$111.72	$111.70	$111.70
Purchase #5	$135.74	5.713%	$143.4948	$143.49	$143.50	$143.50
Purchase #6	$101.78	3.274%	$105.1123	$105.11	$105.10	$105.10
Purchase #7	$173.46	12.871%	$195.786	$195.79	$195.80	$195.80
7 purchase totals =	$615.52		$671.0634	$671.06	$671.05	$671.10