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	$25.75	13.166%	$29.1402	$29.14	$29.15	$29.10
Purchase #2	$128.88	13.654%	$146.4773	$146.48	$146.50	$146.50
Purchase #3	$208.92	6.808%	$223.1433	$223.14	$223.15	$223.10
Purchase #4	$228.26	8.580%	$247.8447	$247.84	$247.85	$247.80
Purchase #5	$168.87	10.831%	$187.1603	$187.16	$187.15	$187.20
Purchase #6	$76.25	8.174%	$82.4827	$82.48	$82.50	$82.50
Purchase #7	$86.32	12.821%	$97.3871	$97.39	$97.40	$97.40
7 purchase totals =	$923.25		$1,013.6356	$1,013.63	$1,013.70	$1,013.60