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	$146.69	13.561%	$166.5826	$166.58	$166.60	$166.60
Purchase #2	$81.88	8.710%	$89.0117	$89.01	$89.00	$89.00
Purchase #3	$144.41	10.228%	$159.1803	$159.18	$159.20	$159.20
Purchase #4	$25.73	12.253%	$28.8827	$28.88	$28.90	$28.90
Purchase #5	$57.68	7.206%	$61.8364	$61.84	$61.85	$61.80
Purchase #6	$219.39	3.172%	$226.3491	$226.35	$226.35	$226.30
Purchase #7	$95.33	12.653%	$107.3921	$107.39	$107.40	$107.40
7 purchase totals =	$771.11		$839.2349	$839.23	$839.30	$839.20