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	$78.91	11.654%	$88.1062	$88.11	$88.10	$88.10
Purchase #2	$121.78	13.146%	$137.7892	$137.79	$137.80	$137.80
Purchase #3	$138.75	6.823%	$148.2169	$148.22	$148.20	$148.20
Purchase #4	$227.39	4.732%	$238.1501	$238.15	$238.15	$238.20
Purchase #5	$240.63	13.146%	$272.2632	$272.26	$272.25	$272.30
Purchase #6	$250.27	6.196%	$265.7767	$265.78	$265.80	$265.80
Purchase #7	$81.61	8.458%	$88.5126	$88.51	$88.50	$88.50
7 purchase totals =	$1,139.34		$1,238.8149	$1,238.82	$1,238.80	$1,238.90