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	$172.80	3.727%	$179.2403	$179.24	$179.25	$179.20
Purchase #2	$196.58	12.636%	$221.4198	$221.42	$221.40	$221.40
Purchase #3	$116.44	12.795%	$131.3385	$131.34	$131.35	$131.30
Purchase #4	$26.47	4.737%	$27.7239	$27.72	$27.70	$27.70
Purchase #5	$94.76	6.838%	$101.2397	$101.24	$101.25	$101.20
Purchase #6	$93.92	6.629%	$100.146	$100.15	$100.15	$100.10
Purchase #7	$93.47	13.778%	$106.3483	$106.35	$106.35	$106.30
7 purchase totals =	$794.44		$867.4565	$867.46	$867.45	$867.20