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	$35.37	8.514%	$38.3814	$38.38	$38.40	$38.40
Purchase #2	$120.81	7.394%	$129.7427	$129.74	$129.75	$129.70
Purchase #3	$131.30	10.366%	$144.9106	$144.91	$144.90	$144.90
Purchase #4	$75.60	12.681%	$85.1868	$85.19	$85.20	$85.20
Purchase #5	$116.59	4.129%	$121.404	$121.40	$121.40	$121.40
Purchase #6	$81.60	6.342%	$86.7751	$86.78	$86.80	$86.80
Purchase #7	$72.51	8.798%	$78.8894	$78.89	$78.90	$78.90
7 purchase totals =	$633.78		$685.2900	$685.29	$685.35	$685.30