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	$163.84	13.281%	$185.5996	$185.60	$185.60	$185.60
Purchase #2	$128.27	11.172%	$142.6003	$142.60	$142.60	$142.60
Purchase #3	$241.67	12.816%	$272.6424	$272.64	$272.65	$272.60
Purchase #4	$174.69	7.351%	$187.5315	$187.53	$187.55	$187.50
Purchase #5	$239.37	10.449%	$264.3818	$264.38	$264.40	$264.40
Purchase #6	$185.72	8.176%	$200.9045	$200.90	$200.90	$200.90
Purchase #7	$77.63	11.692%	$86.7065	$86.71	$86.70	$86.70
7 purchase totals =	$1,211.19		$1,340.3666	$1,340.36	$1,340.40	$1,340.30