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	$122.56	11.306%	$136.4166	$136.42	$136.40	$136.40
Purchase #2	$95.88	9.452%	$104.9426	$104.94	$104.95	$104.90
Purchase #3	$35.73	7.121%	$38.2743	$38.27	$38.25	$38.30
Purchase #4	$119.92	9.835%	$131.7141	$131.71	$131.70	$131.70
Purchase #5	$110.79	9.685%	$121.52	$121.52	$121.50	$121.50
Purchase #6	$102.86	12.812%	$116.0384	$116.04	$116.05	$116.00
Purchase #7	$167.83	13.395%	$190.3108	$190.31	$190.30	$190.30
7 purchase totals =	$755.57		$839.2168	$839.21	$839.15	$839.10