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	$188.43	5.688%	$199.1479	$199.15	$199.15	$199.10
Purchase #2	$46.42	11.703%	$51.8525	$51.85	$51.85	$51.90
Purchase #3	$250.73	8.705%	$272.556	$272.56	$272.55	$272.60
Purchase #4	$86.76	10.199%	$95.6087	$95.61	$95.60	$95.60
Purchase #5	$132.68	5.802%	$140.3781	$140.38	$140.40	$140.40
Purchase #6	$25.30	7.673%	$27.2413	$27.24	$27.25	$27.20
Purchase #7	$115.88	13.789%	$131.8587	$131.86	$131.85	$131.90
7 purchase totals =	$846.20		$918.6432	$918.65	$918.65	$918.70