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	$100.25	13.596%	$113.88	$113.88	$113.90	$113.90
Purchase #2	$15.81	11.809%	$17.677	$17.68	$17.70	$17.70
Purchase #3	$55.61	10.582%	$61.4947	$61.49	$61.50	$61.50
Purchase #4	$244.28	13.549%	$277.3775	$277.38	$277.40	$277.40
Purchase #5	$82.47	10.129%	$90.8234	$90.82	$90.80	$90.80
Purchase #6	$32.31	10.300%	$35.6379	$35.64	$35.65	$35.60
Purchase #7	$54.87	9.370%	$60.0113	$60.01	$60.00	$60.00
7 purchase totals =	$585.60		$656.9018	$656.90	$656.95	$656.90