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	$141.81	6.185%	$150.5809	$150.58	$150.60	$150.60
Purchase #2	$197.59	12.699%	$222.682	$222.68	$222.70	$222.70
Purchase #3	$109.95	4.768%	$115.1924	$115.19	$115.20	$115.20
Purchase #4	$57.33	6.170%	$60.8673	$60.87	$60.85	$60.90
Purchase #5	$35.61	9.517%	$38.999	$39.00	$39.00	$39.00
Purchase #6	$128.76	12.301%	$144.5988	$144.60	$144.60	$144.60
Purchase #7	$182.74	7.680%	$196.7744	$196.77	$196.75	$196.80
7 purchase totals =	$853.79		$929.6948	$929.69	$929.70	$929.80