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	$146.82	6.658%	$156.5953	$156.60	$156.60	$156.60
Purchase #2	$250.46	3.208%	$258.4948	$258.49	$258.50	$258.50
Purchase #3	$37.90	9.217%	$41.3932	$41.39	$41.40	$41.40
Purchase #4	$192.32	7.163%	$206.0959	$206.10	$206.10	$206.10
Purchase #5	$225.67	4.830%	$236.5699	$236.57	$236.55	$236.60
Purchase #6	$157.89	13.654%	$179.4483	$179.45	$179.45	$179.40
Purchase #7	$184.82	3.534%	$191.3515	$191.35	$191.35	$191.40
7 purchase totals =	$1,195.88		$1,269.9489	$1,269.95	$1,269.95	$1,270.00