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	$31.32	5.842%	$33.1497	$33.15	$33.15	$33.10
Purchase #2	$82.93	8.804%	$90.2312	$90.23	$90.25	$90.20
Purchase #3	$52.73	5.823%	$55.8005	$55.80	$55.80	$55.80
Purchase #4	$111.34	10.561%	$123.0986	$123.10	$123.10	$123.10
Purchase #5	$150.25	7.651%	$161.7456	$161.75	$161.75	$161.70
Purchase #6	$115.69	3.797%	$120.0827	$120.08	$120.10	$120.10
Purchase #7	$246.98	11.811%	$276.1508	$276.15	$276.15	$276.20
7 purchase totals =	$791.24		$860.2591	$860.26	$860.30	$860.20