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	$102.53	12.703%	$115.5544	$115.55	$115.55	$115.60
Purchase #2	$128.44	13.353%	$145.5906	$145.59	$145.60	$145.60
Purchase #3	$34.61	4.444%	$36.1481	$36.15	$36.15	$36.10
Purchase #4	$46.47	13.744%	$52.8568	$52.86	$52.85	$52.90
Purchase #5	$210.56	8.178%	$227.7796	$227.78	$227.80	$227.80
Purchase #6	$38.32	11.678%	$42.795	$42.80	$42.80	$42.80
Purchase #7	$222.47	12.785%	$250.9128	$250.91	$250.90	$250.90
7 purchase totals =	$783.40		$871.6373	$871.64	$871.65	$871.70