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	$55.66	4.755%	$58.3066	$58.31	$58.30	$58.30
Purchase #2	$79.82	8.800%	$86.8442	$86.84	$86.85	$86.80
Purchase #3	$140.34	9.608%	$153.8239	$153.82	$153.80	$153.80
Purchase #4	$28.93	9.124%	$31.5696	$31.57	$31.55	$31.60
Purchase #5	$23.90	5.651%	$25.2506	$25.25	$25.25	$25.30
Purchase #6	$160.61	7.189%	$172.1563	$172.16	$172.15	$172.20
Purchase #7	$110.97	11.398%	$123.6184	$123.62	$123.60	$123.60
7 purchase totals =	$600.23		$651.5696	$651.57	$651.50	$651.60