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	$82.42	10.227%	$90.8491	$90.85	$90.85	$90.80
Purchase #2	$229.64	5.775%	$242.9017	$242.90	$242.90	$242.90
Purchase #3	$32.90	7.446%	$35.3497	$35.35	$35.35	$35.30
Purchase #4	$47.51	4.463%	$49.6304	$49.63	$49.65	$49.60
Purchase #5	$124.63	11.632%	$139.127	$139.13	$139.15	$139.10
Purchase #6	$168.94	10.833%	$187.2413	$187.24	$187.25	$187.20
Purchase #7	$206.43	13.503%	$234.3042	$234.30	$234.30	$234.30
7 purchase totals =	$892.47		$979.4034	$979.40	$979.45	$979.20