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	$89.69	3.260%	$92.6139	$92.61	$92.60	$92.60
Purchase #2	$178.37	6.154%	$189.3469	$189.35	$189.35	$189.30
Purchase #3	$103.44	5.837%	$109.4778	$109.48	$109.50	$109.50
Purchase #4	$58.38	13.782%	$66.4259	$66.43	$66.45	$66.40
Purchase #5	$98.91	5.338%	$104.1898	$104.19	$104.20	$104.20
Purchase #6	$25.51	9.192%	$27.8549	$27.85	$27.85	$27.90
Purchase #7	$123.35	11.321%	$137.3145	$137.31	$137.30	$137.30
7 purchase totals =	$677.65		$727.2237	$727.22	$727.25	$727.20