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	$77.93	9.244%	$85.1338	$85.13	$85.15	$85.10
Purchase #2	$141.54	9.237%	$154.614	$154.61	$154.60	$154.60
Purchase #3	$19.87	4.752%	$20.8142	$20.81	$20.80	$20.80
Purchase #4	$126.44	10.296%	$139.4583	$139.46	$139.45	$139.50
Purchase #5	$197.44	6.821%	$210.9074	$210.91	$210.90	$210.90
Purchase #6	$45.89	4.814%	$48.0991	$48.10	$48.10	$48.10
Purchase #7	$219.53	6.374%	$233.5228	$233.52	$233.50	$233.50
7 purchase totals =	$828.64		$892.5496	$892.54	$892.50	$892.50