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	$115.53	5.397%	$121.7652	$121.77	$121.75	$121.80
Purchase #2	$47.43	5.275%	$49.9319	$49.93	$49.95	$49.90
Purchase #3	$139.87	6.239%	$148.5965	$148.60	$148.60	$148.60
Purchase #4	$175.76	5.712%	$185.7994	$185.80	$185.80	$185.80
Purchase #5	$169.92	12.705%	$191.5083	$191.51	$191.50	$191.50
Purchase #6	$51.73	7.478%	$55.5984	$55.60	$55.60	$55.60
Purchase #7	$12.63	3.421%	$13.0621	$13.06	$13.05	$13.10
7 purchase totals =	$712.87		$766.2618	$766.27	$766.25	$766.30