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	$145.68	11.395%	$162.2802	$162.28	$162.30	$162.30
Purchase #2	$217.55	4.455%	$227.2419	$227.24	$227.25	$227.20
Purchase #3	$152.39	10.279%	$168.0542	$168.05	$168.05	$168.10
Purchase #4	$9.25	6.327%	$9.8352	$9.84	$9.85	$9.80
Purchase #5	$56.40	4.847%	$59.1337	$59.13	$59.15	$59.10
Purchase #6	$137.53	3.175%	$141.8966	$141.90	$141.90	$141.90
Purchase #7	$86.75	3.252%	$89.5711	$89.57	$89.55	$89.60
7 purchase totals =	$805.55		$858.0129	$858.01	$858.05	$858.00