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	$174.46	3.221%	$180.0794	$180.08	$180.10	$180.10
Purchase #2	$181.30	8.426%	$196.5763	$196.58	$196.60	$196.60
Purchase #3	$53.91	6.408%	$57.3646	$57.36	$57.35	$57.40
Purchase #4	$96.82	5.531%	$102.1751	$102.18	$102.20	$102.20
Purchase #5	$105.38	13.852%	$119.9772	$119.98	$120.00	$120.00
Purchase #6	$191.83	4.504%	$200.47	$200.47	$200.45	$200.50
Purchase #7	$103.56	11.809%	$115.7894	$115.79	$115.80	$115.80
7 purchase totals =	$907.26		$972.4320	$972.44	$972.50	$972.60