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	$247.25	3.102%	$254.9197	$254.92	$254.90	$254.90
Purchase #2	$93.61	7.444%	$100.5783	$100.58	$100.60	$100.60
Purchase #3	$72.38	12.699%	$81.5715	$81.57	$81.55	$81.60
Purchase #4	$102.96	12.542%	$115.8732	$115.87	$115.85	$115.90
Purchase #5	$182.34	4.712%	$190.9319	$190.93	$190.95	$190.90
Purchase #6	$213.49	7.802%	$230.1465	$230.15	$230.15	$230.10
Purchase #7	$88.81	10.286%	$97.945	$97.95	$97.95	$97.90
7 purchase totals =	$1,000.84		$1,071.9661	$1,071.97	$1,071.95	$1,071.90