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	$92.51	7.669%	$99.6046	$99.60	$99.60	$99.60
Purchase #2	$187.60	5.745%	$198.3776	$198.38	$198.40	$198.40
Purchase #3	$20.77	10.544%	$22.96	$22.96	$22.95	$23.00
Purchase #4	$97.71	5.491%	$103.0753	$103.08	$103.10	$103.10
Purchase #5	$93.92	7.621%	$101.0776	$101.08	$101.10	$101.10
Purchase #6	$188.69	4.127%	$196.4772	$196.48	$196.50	$196.50
Purchase #7	$200.73	13.869%	$228.5692	$228.57	$228.55	$228.60
7 purchase totals =	$881.93		$950.1415	$950.15	$950.20	$950.30