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	$48.96	12.586%	$55.1221	$55.12	$55.10	$55.10
Purchase #2	$41.59	3.619%	$43.0951	$43.10	$43.10	$43.10
Purchase #3	$242.53	9.827%	$266.3634	$266.36	$266.35	$266.40
Purchase #4	$84.50	6.698%	$90.1598	$90.16	$90.15	$90.20
Purchase #5	$81.99	8.703%	$89.1256	$89.13	$89.15	$89.10
Purchase #6	$30.59	6.144%	$32.4694	$32.47	$32.45	$32.50
Purchase #7	$248.75	11.697%	$277.8463	$277.85	$277.85	$277.80
7 purchase totals =	$778.91		$854.1817	$854.19	$854.15	$854.20