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	$56.37	6.242%	$59.8886	$59.89	$59.90	$59.90
Purchase #2	$172.27	13.734%	$195.9296	$195.93	$195.95	$195.90
Purchase #3	$55.84	13.315%	$63.2751	$63.28	$63.30	$63.30
Purchase #4	$139.79	3.384%	$144.5205	$144.52	$144.50	$144.50
Purchase #5	$74.25	9.812%	$81.5354	$81.54	$81.55	$81.50
Purchase #6	$161.72	3.178%	$166.8595	$166.86	$166.85	$166.90
Purchase #7	$164.62	12.494%	$185.1876	$185.19	$185.20	$185.20
7 purchase totals =	$824.86		$897.1963	$897.21	$897.25	$897.20