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	$9.51	8.765%	$10.3436	$10.34	$10.35	$10.30
Purchase #2	$81.66	10.651%	$90.3576	$90.36	$90.35	$90.40
Purchase #3	$179.34	10.743%	$198.6065	$198.61	$198.60	$198.60
Purchase #4	$99.58	3.314%	$102.8801	$102.88	$102.90	$102.90
Purchase #5	$224.37	9.332%	$245.3082	$245.31	$245.30	$245.30
Purchase #6	$136.45	7.208%	$146.2853	$146.29	$146.30	$146.30
Purchase #7	$167.90	10.303%	$185.1987	$185.20	$185.20	$185.20
7 purchase totals =	$898.81		$978.9800	$978.99	$979.00	$979.00