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	$103.51	12.446%	$116.3929	$116.39	$116.40	$116.40
Purchase #2	$66.43	7.835%	$71.6348	$71.63	$71.65	$71.60
Purchase #3	$114.88	11.482%	$128.0705	$128.07	$128.05	$128.10
Purchase #4	$202.63	9.653%	$222.1899	$222.19	$222.20	$222.20
Purchase #5	$48.91	5.214%	$51.4602	$51.46	$51.45	$51.50
Purchase #6	$209.94	6.411%	$223.3993	$223.40	$223.40	$223.40
Purchase #7	$61.27	8.260%	$66.3309	$66.33	$66.35	$66.30
7 purchase totals =	$807.57		$879.4785	$879.47	$879.50	$879.50