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	$99.30	8.660%	$107.8994	$107.90	$107.90	$107.90
Purchase #2	$117.51	11.376%	$130.8779	$130.88	$130.90	$130.90
Purchase #3	$165.38	3.723%	$171.5371	$171.54	$171.55	$171.50
Purchase #4	$168.33	12.369%	$189.1507	$189.15	$189.15	$189.20
Purchase #5	$239.58	9.287%	$261.8298	$261.83	$261.85	$261.80
Purchase #6	$63.69	13.783%	$72.4684	$72.47	$72.45	$72.50
Purchase #7	$121.48	13.833%	$138.2843	$138.28	$138.30	$138.30
7 purchase totals =	$975.27		$1,072.0476	$1,072.05	$1,072.10	$1,072.10