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	$231.63	4.679%	$242.468	$242.47	$242.45	$242.50
Purchase #2	$191.71	3.191%	$197.8275	$197.83	$197.85	$197.80
Purchase #3	$52.48	12.698%	$59.1439	$59.14	$59.15	$59.10
Purchase #4	$170.37	8.482%	$184.8208	$184.82	$184.80	$184.80
Purchase #5	$188.78	11.408%	$210.316	$210.32	$210.30	$210.30
Purchase #6	$123.25	9.215%	$134.6075	$134.61	$134.60	$134.60
Purchase #7	$20.53	5.287%	$21.6154	$21.62	$21.60	$21.60
7 purchase totals =	$978.75		$1,050.7991	$1,050.81	$1,050.75	$1,050.70