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	$61.71	9.497%	$67.5706	$67.57	$67.55	$67.60
Purchase #2	$85.44	6.238%	$90.7697	$90.77	$90.75	$90.80
Purchase #3	$84.30	10.176%	$92.8784	$92.88	$92.90	$92.90
Purchase #4	$99.47	4.107%	$103.5552	$103.56	$103.55	$103.60
Purchase #5	$213.69	3.548%	$221.2717	$221.27	$221.25	$221.30
Purchase #6	$73.35	9.264%	$80.1451	$80.15	$80.15	$80.10
Purchase #7	$52.56	8.357%	$56.9524	$56.95	$56.95	$57.00
7 purchase totals =	$670.52		$713.1431	$713.15	$713.10	$713.30