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	$138.84	8.371%	$150.4623	$150.46	$150.45	$150.50
Purchase #2	$33.91	4.694%	$35.5017	$35.50	$35.50	$35.50
Purchase #3	$225.59	12.823%	$254.5174	$254.52	$254.50	$254.50
Purchase #4	$113.73	8.780%	$123.7155	$123.72	$123.70	$123.70
Purchase #5	$101.90	8.537%	$110.5992	$110.60	$110.60	$110.60
Purchase #6	$23.85	8.270%	$25.8224	$25.82	$25.80	$25.80
Purchase #7	$5.72	9.421%	$6.2589	$6.26	$6.25	$6.30
7 purchase totals =	$643.54		$706.8774	$706.88	$706.80	$706.90