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	$47.45	6.791%	$50.6723	$50.67	$50.65	$50.70
Purchase #2	$98.57	13.312%	$111.6916	$111.69	$111.70	$111.70
Purchase #3	$135.86	13.791%	$154.5965	$154.60	$154.60	$154.60
Purchase #4	$222.42	8.303%	$240.8875	$240.89	$240.90	$240.90
Purchase #5	$107.81	6.714%	$115.0484	$115.05	$115.05	$115.00
Purchase #6	$41.27	10.872%	$45.7569	$45.76	$45.75	$45.80
Purchase #7	$106.38	9.385%	$116.3638	$116.36	$116.35	$116.40
7 purchase totals =	$759.76		$835.0170	$835.02	$835.00	$835.10