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	$83.41	7.680%	$89.8159	$89.82	$89.80	$89.80
Purchase #2	$210.42	10.220%	$231.9249	$231.92	$231.90	$231.90
Purchase #3	$62.48	9.527%	$68.4325	$68.43	$68.45	$68.40
Purchase #4	$143.89	11.616%	$160.6043	$160.60	$160.60	$160.60
Purchase #5	$192.32	11.486%	$214.4099	$214.41	$214.40	$214.40
Purchase #6	$91.80	7.470%	$98.6575	$98.66	$98.65	$98.70
Purchase #7	$211.81	7.361%	$227.4013	$227.40	$227.40	$227.40
7 purchase totals =	$996.13		$1,091.2463	$1,091.24	$1,091.20	$1,091.20