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	$74.45	5.815%	$78.7793	$78.78	$78.80	$78.80
Purchase #2	$94.41	12.672%	$106.3736	$106.37	$106.35	$106.40
Purchase #3	$156.88	5.251%	$165.1178	$165.12	$165.10	$165.10
Purchase #4	$174.76	5.526%	$184.4172	$184.42	$184.40	$184.40
Purchase #5	$165.93	3.681%	$172.0379	$172.04	$172.05	$172.00
Purchase #6	$160.95	5.528%	$169.8473	$169.85	$169.85	$169.80
Purchase #7	$29.52	10.571%	$32.6406	$32.64	$32.65	$32.60
7 purchase totals =	$856.90		$909.2137	$909.22	$909.20	$909.10