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	$109.82	10.571%	$121.4291	$121.43	$121.45	$121.40
Purchase #2	$210.58	6.257%	$223.756	$223.76	$223.75	$223.80
Purchase #3	$192.39	4.396%	$200.8475	$200.85	$200.85	$200.80
Purchase #4	$83.55	7.721%	$90.0009	$90.00	$90.00	$90.00
Purchase #5	$224.67	13.799%	$255.6722	$255.67	$255.65	$255.70
Purchase #6	$86.62	4.120%	$90.1887	$90.19	$90.20	$90.20
Purchase #7	$131.58	6.749%	$140.4603	$140.46	$140.45	$140.50
7 purchase totals =	$1,039.21		$1,122.3547	$1,122.36	$1,122.35	$1,122.40