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	$21.92	8.847%	$23.8593	$23.86	$23.85	$23.90
Purchase #2	$99.48	5.430%	$104.8818	$104.88	$104.90	$104.90
Purchase #3	$52.62	7.172%	$56.3939	$56.39	$56.40	$56.40
Purchase #4	$79.31	12.801%	$89.4625	$89.46	$89.45	$89.50
Purchase #5	$234.39	5.109%	$246.365	$246.37	$246.35	$246.40
Purchase #6	$136.33	11.343%	$151.7939	$151.79	$151.80	$151.80
Purchase #7	$154.35	9.761%	$169.4161	$169.42	$169.40	$169.40
7 purchase totals =	$778.40		$842.1725	$842.17	$842.15	$842.30