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	$105.49	9.865%	$115.8966	$115.90	$115.90	$115.90
Purchase #2	$41.50	9.396%	$45.3993	$45.40	$45.40	$45.40
Purchase #3	$179.43	13.164%	$203.0502	$203.05	$203.05	$203.10
Purchase #4	$163.25	7.412%	$175.3501	$175.35	$175.35	$175.40
Purchase #5	$148.27	5.205%	$155.9875	$155.99	$156.00	$156.00
Purchase #6	$180.39	9.167%	$196.9264	$196.93	$196.95	$196.90
Purchase #7	$45.92	6.393%	$48.8557	$48.86	$48.85	$48.90
7 purchase totals =	$864.25		$941.4658	$941.48	$941.50	$941.60