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	$249.45	8.347%	$270.2716	$270.27	$270.25	$270.30
Purchase #2	$13.45	6.871%	$14.3741	$14.37	$14.35	$14.40
Purchase #3	$179.53	7.285%	$192.6088	$192.61	$192.60	$192.60
Purchase #4	$59.48	13.514%	$67.5181	$67.52	$67.50	$67.50
Purchase #5	$24.40	13.548%	$27.7057	$27.71	$27.70	$27.70
Purchase #6	$186.46	6.821%	$199.1784	$199.18	$199.20	$199.20
Purchase #7	$244.25	12.740%	$275.3675	$275.37	$275.35	$275.40
7 purchase totals =	$957.02		$1,047.0242	$1,047.03	$1,046.95	$1,047.10