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	$26.81	6.636%	$28.5891	$28.59	$28.60	$28.60
Purchase #2	$91.62	12.725%	$103.2786	$103.28	$103.30	$103.30
Purchase #3	$5.86	7.667%	$6.3093	$6.31	$6.30	$6.30
Purchase #4	$197.31	13.206%	$223.3668	$223.37	$223.35	$223.40
Purchase #5	$65.61	4.418%	$68.5086	$68.51	$68.50	$68.50
Purchase #6	$35.66	8.780%	$38.7909	$38.79	$38.80	$38.80
Purchase #7	$77.47	7.787%	$83.5026	$83.50	$83.50	$83.50
7 purchase totals =	$500.34		$552.3459	$552.35	$552.35	$552.40