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	$85.39	5.490%	$90.0779	$90.08	$90.10	$90.10
Purchase #2	$92.28	6.496%	$98.2745	$98.27	$98.25	$98.30
Purchase #3	$130.54	7.655%	$140.5328	$140.53	$140.55	$140.50
Purchase #4	$191.51	6.718%	$204.3756	$204.38	$204.40	$204.40
Purchase #5	$104.83	10.133%	$115.4524	$115.45	$115.45	$115.50
Purchase #6	$37.97	10.279%	$41.8729	$41.87	$41.85	$41.90
Purchase #7	$49.57	4.765%	$51.932	$51.93	$51.95	$51.90
7 purchase totals =	$692.09		$742.5181	$742.51	$742.55	$742.60