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	$40.45	12.646%	$45.5653	$45.57	$45.55	$45.60
Purchase #2	$193.86	8.193%	$209.7429	$209.74	$209.75	$209.70
Purchase #3	$107.69	7.757%	$116.0435	$116.04	$116.05	$116.00
Purchase #4	$160.92	6.638%	$171.6019	$171.60	$171.60	$171.60
Purchase #5	$197.32	13.235%	$223.4353	$223.44	$223.45	$223.40
Purchase #6	$185.29	3.503%	$191.7807	$191.78	$191.80	$191.80
Purchase #7	$173.25	4.778%	$181.5279	$181.53	$181.55	$181.50
7 purchase totals =	$1,058.78		$1,139.6975	$1,139.70	$1,139.75	$1,139.60