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	$100.45	12.357%	$112.8626	$112.86	$112.85	$112.90
Purchase #2	$159.82	11.633%	$178.4119	$178.41	$178.40	$178.40
Purchase #3	$40.56	12.798%	$45.7509	$45.75	$45.75	$45.80
Purchase #4	$128.90	12.505%	$145.0189	$145.02	$145.00	$145.00
Purchase #5	$137.44	10.522%	$151.9014	$151.90	$151.90	$151.90
Purchase #6	$95.56	6.244%	$101.5268	$101.53	$101.55	$101.50
Purchase #7	$90.97	10.320%	$100.3581	$100.36	$100.35	$100.40
7 purchase totals =	$753.70		$835.8306	$835.83	$835.80	$835.90