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	$50.77	12.349%	$57.0396	$57.04	$57.05	$57.00
Purchase #2	$224.77	9.387%	$245.8692	$245.87	$245.85	$245.90
Purchase #3	$83.90	10.315%	$92.5543	$92.55	$92.55	$92.60
Purchase #4	$202.91	10.222%	$223.6515	$223.65	$223.65	$223.70
Purchase #5	$28.73	3.867%	$29.841	$29.84	$29.85	$29.80
Purchase #6	$148.57	10.605%	$164.3258	$164.33	$164.35	$164.30
Purchase #7	$90.38	13.517%	$102.5967	$102.60	$102.60	$102.60
7 purchase totals =	$830.03		$915.8781	$915.88	$915.90	$915.90