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	$85.74	12.798%	$96.713	$96.71	$96.70	$96.70
Purchase #2	$158.90	4.556%	$166.1395	$166.14	$166.15	$166.10
Purchase #3	$225.62	13.849%	$256.8661	$256.87	$256.85	$256.90
Purchase #4	$111.56	3.756%	$115.7502	$115.75	$115.75	$115.80
Purchase #5	$224.67	13.723%	$255.5015	$255.50	$255.50	$255.50
Purchase #6	$81.78	9.235%	$89.3324	$89.33	$89.35	$89.30
Purchase #7	$49.47	8.775%	$53.811	$53.81	$53.80	$53.80
7 purchase totals =	$937.74		$1,034.1137	$1,034.11	$1,034.10	$1,034.10