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	$134.72	5.677%	$142.3681	$142.37	$142.35	$142.40
Purchase #2	$205.76	12.342%	$231.1549	$231.15	$231.15	$231.20
Purchase #3	$148.69	12.630%	$167.4695	$167.47	$167.45	$167.50
Purchase #4	$91.38	4.672%	$95.6493	$95.65	$95.65	$95.60
Purchase #5	$186.80	5.838%	$197.7054	$197.71	$197.70	$197.70
Purchase #6	$160.65	8.511%	$174.3229	$174.32	$174.30	$174.30
Purchase #7	$81.33	12.395%	$91.4109	$91.41	$91.40	$91.40
7 purchase totals =	$1,009.33		$1,100.0810	$1,100.08	$1,100.00	$1,100.10