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	$21.38	6.638%	$22.7992	$22.80	$22.80	$22.80
Purchase #2	$23.84	13.597%	$27.0815	$27.08	$27.10	$27.10
Purchase #3	$242.29	10.248%	$267.1199	$267.12	$267.10	$267.10
Purchase #4	$77.48	6.229%	$82.3062	$82.31	$82.30	$82.30
Purchase #5	$81.89	10.263%	$90.2944	$90.29	$90.30	$90.30
Purchase #6	$41.70	9.814%	$45.7924	$45.79	$45.80	$45.80
Purchase #7	$114.25	11.337%	$127.2025	$127.20	$127.20	$127.20
7 purchase totals =	$602.83		$662.5961	$662.59	$662.60	$662.60