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	$51.50	7.869%	$55.5525	$55.55	$55.55	$55.60
Purchase #2	$41.60	10.204%	$45.8449	$45.84	$45.85	$45.80
Purchase #3	$39.80	12.325%	$44.7054	$44.71	$44.70	$44.70
Purchase #4	$102.40	12.779%	$115.4857	$115.49	$115.50	$115.50
Purchase #5	$79.60	7.520%	$85.5859	$85.59	$85.60	$85.60
Purchase #6	$102.45	8.523%	$111.1818	$111.18	$111.20	$111.20
Purchase #7	$33.39	8.215%	$36.133	$36.13	$36.15	$36.10
7 purchase totals =	$450.74		$494.4892	$494.49	$494.55	$494.50