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	$10.87	9.267%	$11.8773	$11.88	$11.90	$11.90
Purchase #2	$213.88	11.337%	$238.1276	$238.13	$238.15	$238.10
Purchase #3	$186.92	12.392%	$210.0831	$210.08	$210.10	$210.10
Purchase #4	$152.59	12.551%	$171.7416	$171.74	$171.75	$171.70
Purchase #5	$175.81	11.630%	$196.2567	$196.26	$196.25	$196.30
Purchase #6	$153.99	7.473%	$165.4977	$165.50	$165.50	$165.50
Purchase #7	$187.55	8.272%	$203.0641	$203.06	$203.05	$203.10
7 purchase totals =	$1,081.61		$1,196.6481	$1,196.65	$1,196.70	$1,196.70