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	$109.31	12.607%	$123.0907	$123.09	$123.10	$123.10
Purchase #2	$28.32	10.613%	$31.3256	$31.33	$31.35	$31.30
Purchase #3	$91.95	11.390%	$102.4231	$102.42	$102.40	$102.40
Purchase #4	$196.98	13.567%	$223.7043	$223.70	$223.70	$223.70
Purchase #5	$21.30	7.599%	$22.9186	$22.92	$22.90	$22.90
Purchase #6	$110.31	7.393%	$118.4652	$118.47	$118.45	$118.50
Purchase #7	$86.46	13.572%	$98.1944	$98.19	$98.20	$98.20
7 purchase totals =	$644.63		$720.1219	$720.12	$720.10	$720.10