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	$83.61	8.245%	$90.5036	$90.50	$90.50	$90.50
Purchase #2	$19.25	13.215%	$21.7939	$21.79	$21.80	$21.80
Purchase #3	$40.86	7.548%	$43.9441	$43.94	$43.95	$43.90
Purchase #4	$35.76	4.322%	$37.3055	$37.31	$37.30	$37.30
Purchase #5	$115.85	6.496%	$123.3756	$123.38	$123.40	$123.40
Purchase #6	$140.86	5.704%	$148.8947	$148.89	$148.90	$148.90
Purchase #7	$120.46	5.585%	$127.1877	$127.19	$127.20	$127.20
7 purchase totals =	$556.65		$593.0051	$593.00	$593.05	$593.00