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	$233.95	6.720%	$249.6714	$249.67	$249.65	$249.70
Purchase #2	$85.98	4.578%	$89.9162	$89.92	$89.90	$89.90
Purchase #3	$209.91	10.682%	$232.3326	$232.33	$232.35	$232.30
Purchase #4	$55.49	9.612%	$60.8237	$60.82	$60.80	$60.80
Purchase #5	$90.94	13.827%	$103.5143	$103.51	$103.50	$103.50
Purchase #6	$59.46	9.434%	$65.0695	$65.07	$65.05	$65.10
Purchase #7	$61.95	13.203%	$70.1293	$70.13	$70.15	$70.10
7 purchase totals =	$797.68		$871.4570	$871.45	$871.40	$871.40