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	$26.42	11.250%	$29.3923	$29.39	$29.40	$29.40
Purchase #2	$86.42	9.185%	$94.3577	$94.36	$94.35	$94.40
Purchase #3	$29.27	9.806%	$32.1402	$32.14	$32.15	$32.10
Purchase #4	$192.72	10.108%	$212.2001	$212.20	$212.20	$212.20
Purchase #5	$82.81	7.799%	$89.2684	$89.27	$89.25	$89.30
Purchase #6	$135.33	4.709%	$141.7027	$141.70	$141.70	$141.70
Purchase #7	$66.45	3.179%	$68.5624	$68.56	$68.55	$68.60
7 purchase totals =	$619.42		$667.6238	$667.62	$667.60	$667.70