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	$242.91	9.293%	$265.4836	$265.48	$265.50	$265.50
Purchase #2	$14.76	12.471%	$16.6007	$16.60	$16.60	$16.60
Purchase #3	$24.67	12.695%	$27.8019	$27.80	$27.80	$27.80
Purchase #4	$120.51	9.231%	$131.6343	$131.63	$131.65	$131.60
Purchase #5	$76.28	7.646%	$82.1124	$82.11	$82.10	$82.10
Purchase #6	$113.89	12.340%	$127.944	$127.94	$127.95	$127.90
Purchase #7	$20.87	8.734%	$22.6928	$22.69	$22.70	$22.70
7 purchase totals =	$613.89		$674.2697	$674.25	$674.30	$674.20