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	$121.82	4.279%	$127.0327	$127.03	$127.05	$127.00
Purchase #2	$20.41	10.187%	$22.4892	$22.49	$22.50	$22.50
Purchase #3	$80.88	12.295%	$90.8242	$90.82	$90.80	$90.80
Purchase #4	$164.67	4.617%	$172.2728	$172.27	$172.25	$172.30
Purchase #5	$73.30	13.285%	$83.0379	$83.04	$83.05	$83.00
Purchase #6	$128.37	3.688%	$133.1043	$133.10	$133.10	$133.10
Purchase #7	$5.81	12.713%	$6.5486	$6.55	$6.55	$6.50
7 purchase totals =	$595.26		$635.3097	$635.30	$635.30	$635.20