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	$226.55	13.788%	$257.7867	$257.79	$257.80	$257.80
Purchase #2	$49.38	13.228%	$55.912	$55.91	$55.90	$55.90
Purchase #3	$90.64	11.280%	$100.8642	$100.86	$100.85	$100.90
Purchase #4	$247.62	10.361%	$273.2759	$273.28	$273.30	$273.30
Purchase #5	$22.66	10.464%	$25.0311	$25.03	$25.05	$25.00
Purchase #6	$199.25	12.504%	$224.1642	$224.16	$224.15	$224.20
Purchase #7	$103.87	8.102%	$112.2855	$112.29	$112.30	$112.30
7 purchase totals =	$939.97		$1,049.3196	$1,049.32	$1,049.35	$1,049.40