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	$43.71	8.282%	$47.3301	$47.33	$47.35	$47.30
Purchase #2	$220.99	9.859%	$242.7774	$242.78	$242.80	$242.80
Purchase #3	$37.42	7.404%	$40.1906	$40.19	$40.20	$40.20
Purchase #4	$182.83	7.544%	$196.6227	$196.62	$196.60	$196.60
Purchase #5	$80.56	10.868%	$89.3153	$89.32	$89.30	$89.30
Purchase #6	$61.99	13.214%	$70.1814	$70.18	$70.20	$70.20
Purchase #7	$128.81	6.178%	$136.7679	$136.77	$136.75	$136.80
7 purchase totals =	$756.31		$823.1854	$823.19	$823.20	$823.20