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	$147.57	12.839%	$166.5165	$166.52	$166.50	$166.50
Purchase #2	$101.38	10.369%	$111.8921	$111.89	$111.90	$111.90
Purchase #3	$6.63	6.862%	$7.085	$7.09	$7.10	$7.10
Purchase #4	$7.42	8.408%	$8.0439	$8.04	$8.05	$8.00
Purchase #5	$193.39	11.777%	$216.1655	$216.17	$216.15	$216.20
Purchase #6	$245.45	7.526%	$263.9226	$263.92	$263.90	$263.90
Purchase #7	$14.46	5.633%	$15.2745	$15.27	$15.25	$15.30
7 purchase totals =	$716.30		$788.9001	$788.90	$788.85	$788.90