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	$246.68	11.551%	$275.174	$275.17	$275.15	$275.20
Purchase #2	$81.88	10.374%	$90.3742	$90.37	$90.35	$90.40
Purchase #3	$59.64	11.317%	$66.3895	$66.39	$66.40	$66.40
Purchase #4	$38.53	6.104%	$40.8819	$40.88	$40.90	$40.90
Purchase #5	$210.59	3.649%	$218.2744	$218.27	$218.25	$218.30
Purchase #6	$56.66	12.845%	$63.938	$63.94	$63.95	$63.90
Purchase #7	$159.29	7.407%	$171.0886	$171.09	$171.10	$171.10
7 purchase totals =	$853.27		$926.1206	$926.11	$926.10	$926.20