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	$250.35	13.534%	$284.2324	$284.23	$284.25	$284.20
Purchase #2	$59.79	5.232%	$62.9182	$62.92	$62.90	$62.90
Purchase #3	$126.39	5.349%	$133.1506	$133.15	$133.15	$133.20
Purchase #4	$89.27	9.241%	$97.5194	$97.52	$97.50	$97.50
Purchase #5	$142.34	11.303%	$158.4287	$158.43	$158.45	$158.40
Purchase #6	$141.75	7.340%	$152.1545	$152.15	$152.15	$152.20
Purchase #7	$211.32	13.790%	$240.461	$240.46	$240.45	$240.50
7 purchase totals =	$1,021.21		$1,128.8648	$1,128.86	$1,128.85	$1,128.90