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	$64.58	12.774%	$72.8294	$72.83	$72.85	$72.80
Purchase #2	$46.30	7.798%	$49.9105	$49.91	$49.90	$49.90
Purchase #3	$246.53	9.364%	$269.6151	$269.62	$269.60	$269.60
Purchase #4	$109.28	4.560%	$114.2632	$114.26	$114.25	$114.30
Purchase #5	$31.68	5.598%	$33.4534	$33.45	$33.45	$33.50
Purchase #6	$61.86	4.120%	$64.4086	$64.41	$64.40	$64.40
Purchase #7	$59.90	10.581%	$66.238	$66.24	$66.25	$66.20
7 purchase totals =	$620.13		$670.7182	$670.72	$670.70	$670.70