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	$11.92	3.606%	$12.3498	$12.35	$12.35	$12.30
Purchase #2	$61.32	8.592%	$66.5886	$66.59	$66.60	$66.60
Purchase #3	$81.33	6.837%	$86.8905	$86.89	$86.90	$86.90
Purchase #4	$225.91	12.178%	$253.4213	$253.42	$253.40	$253.40
Purchase #5	$172.73	8.171%	$186.8438	$186.84	$186.85	$186.80
Purchase #6	$242.46	13.874%	$276.0989	$276.10	$276.10	$276.10
Purchase #7	$78.61	5.751%	$83.1309	$83.13	$83.15	$83.10
7 purchase totals =	$874.28		$965.3238	$965.32	$965.35	$965.20