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	$29.95	7.864%	$32.3053	$32.31	$32.30	$32.30
Purchase #2	$180.77	4.828%	$189.4976	$189.50	$189.50	$189.50
Purchase #3	$181.58	8.321%	$196.6893	$196.69	$196.70	$196.70
Purchase #4	$35.50	12.278%	$39.8587	$39.86	$39.85	$39.90
Purchase #5	$67.61	12.822%	$76.279	$76.28	$76.30	$76.30
Purchase #6	$47.43	6.593%	$50.5571	$50.56	$50.55	$50.60
Purchase #7	$24.42	11.873%	$27.3194	$27.32	$27.30	$27.30
7 purchase totals =	$567.26		$612.5064	$612.52	$612.50	$612.60