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	$98.66	13.116%	$111.6002	$111.60	$111.60	$111.60
Purchase #2	$117.30	9.800%	$128.7954	$128.80	$128.80	$128.80
Purchase #3	$65.48	9.831%	$71.9173	$71.92	$71.90	$71.90
Purchase #4	$183.57	10.816%	$203.4249	$203.42	$203.40	$203.40
Purchase #5	$175.92	4.540%	$183.9068	$183.91	$183.90	$183.90
Purchase #6	$172.71	9.664%	$189.4007	$189.40	$189.40	$189.40
Purchase #7	$10.82	5.544%	$11.4199	$11.42	$11.40	$11.40
7 purchase totals =	$824.46		$900.4652	$900.47	$900.40	$900.40