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	$18.96	4.828%	$19.8754	$19.88	$19.90	$19.90
Purchase #2	$127.46	11.649%	$142.3078	$142.31	$142.30	$142.30
Purchase #3	$57.46	13.380%	$65.1481	$65.15	$65.15	$65.10
Purchase #4	$66.30	9.634%	$72.6873	$72.69	$72.70	$72.70
Purchase #5	$242.66	13.336%	$275.0211	$275.02	$275.00	$275.00
Purchase #6	$74.33	10.431%	$82.0834	$82.08	$82.10	$82.10
Purchase #7	$170.94	8.257%	$185.0545	$185.05	$185.05	$185.10
7 purchase totals =	$758.11		$842.1776	$842.18	$842.20	$842.20