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	$117.93	11.415%	$131.3917	$131.39	$131.40	$131.40
Purchase #2	$139.31	9.675%	$152.7882	$152.79	$152.80	$152.80
Purchase #3	$95.92	8.151%	$103.7384	$103.74	$103.75	$103.70
Purchase #4	$224.79	6.160%	$238.6371	$238.64	$238.65	$238.60
Purchase #5	$69.70	5.139%	$73.2819	$73.28	$73.30	$73.30
Purchase #6	$139.97	5.678%	$147.9175	$147.92	$147.90	$147.90
Purchase #7	$96.81	12.758%	$109.161	$109.16	$109.15	$109.20
7 purchase totals =	$884.43		$956.9158	$956.92	$956.95	$956.90