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	$24.96	13.790%	$28.402	$28.40	$28.40	$28.40
Purchase #2	$192.54	9.181%	$210.2171	$210.22	$210.20	$210.20
Purchase #3	$128.79	9.831%	$141.4513	$141.45	$141.45	$141.50
Purchase #4	$102.37	10.823%	$113.4495	$113.45	$113.45	$113.40
Purchase #5	$178.80	9.120%	$195.1066	$195.11	$195.10	$195.10
Purchase #6	$96.58	13.404%	$109.5256	$109.53	$109.55	$109.50
Purchase #7	$92.86	8.449%	$100.7057	$100.71	$100.70	$100.70
7 purchase totals =	$816.90		$898.8578	$898.87	$898.85	$898.80