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	$31.94	13.761%	$36.3353	$36.34	$36.35	$36.30
Purchase #2	$121.87	13.552%	$138.3858	$138.39	$138.40	$138.40
Purchase #3	$122.52	7.538%	$131.7556	$131.76	$131.75	$131.80
Purchase #4	$71.48	9.709%	$78.42	$78.42	$78.40	$78.40
Purchase #5	$18.46	4.522%	$19.2948	$19.29	$19.30	$19.30
Purchase #6	$68.94	11.566%	$76.9136	$76.91	$76.90	$76.90
Purchase #7	$175.33	13.850%	$199.6132	$199.61	$199.60	$199.60
7 purchase totals =	$610.54		$680.7183	$680.72	$680.70	$680.70