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	$38.90	11.323%	$43.3046	$43.30	$43.30	$43.30
Purchase #2	$71.44	6.480%	$76.0693	$76.07	$76.05	$76.10
Purchase #3	$143.35	3.282%	$148.0547	$148.05	$148.05	$148.10
Purchase #4	$45.92	11.753%	$51.317	$51.32	$51.30	$51.30
Purchase #5	$231.25	8.133%	$250.0576	$250.06	$250.05	$250.10
Purchase #6	$138.90	3.868%	$144.2727	$144.27	$144.25	$144.30
Purchase #7	$159.77	4.419%	$166.8302	$166.83	$166.85	$166.80
7 purchase totals =	$829.53		$879.9061	$879.90	$879.85	$880.00