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	$77.66	9.866%	$85.3219	$85.32	$85.30	$85.30
Purchase #2	$126.96	12.647%	$143.0166	$143.02	$143.00	$143.00
Purchase #3	$83.41	12.598%	$93.918	$93.92	$93.90	$93.90
Purchase #4	$151.27	13.613%	$171.8624	$171.86	$171.85	$171.90
Purchase #5	$218.91	9.690%	$240.1224	$240.12	$240.10	$240.10
Purchase #6	$177.44	5.731%	$187.6091	$187.61	$187.60	$187.60
Purchase #7	$142.85	12.556%	$160.7862	$160.79	$160.80	$160.80
7 purchase totals =	$978.50		$1,082.6366	$1,082.64	$1,082.55	$1,082.60