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	$43.38	8.294%	$46.9779	$46.98	$47.00	$47.00
Purchase #2	$219.48	4.850%	$230.1248	$230.12	$230.10	$230.10
Purchase #3	$177.48	5.753%	$187.6904	$187.69	$187.70	$187.70
Purchase #4	$39.77	10.389%	$43.9017	$43.90	$43.90	$43.90
Purchase #5	$112.56	9.637%	$123.4074	$123.41	$123.40	$123.40
Purchase #6	$71.42	10.713%	$79.0712	$79.07	$79.05	$79.10
Purchase #7	$166.45	11.674%	$185.8814	$185.88	$185.90	$185.90
7 purchase totals =	$830.54		$897.0548	$897.05	$897.05	$897.10