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	$85.43	5.850%	$90.4277	$90.43	$90.45	$90.40
Purchase #2	$244.66	7.826%	$263.8071	$263.81	$263.80	$263.80
Purchase #3	$139.85	12.182%	$156.8865	$156.89	$156.90	$156.90
Purchase #4	$6.54	4.391%	$6.8272	$6.83	$6.85	$6.80
Purchase #5	$146.58	9.656%	$160.7338	$160.73	$160.75	$160.70
Purchase #6	$10.35	10.499%	$11.4366	$11.44	$11.45	$11.40
Purchase #7	$11.69	4.528%	$12.2193	$12.22	$12.20	$12.20
7 purchase totals =	$645.10		$702.3382	$702.35	$702.40	$702.20