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	$67.77	6.571%	$72.2232	$72.22	$72.20	$72.20
Purchase #2	$39.43	7.743%	$42.4831	$42.48	$42.50	$42.50
Purchase #3	$63.86	10.669%	$70.6732	$70.67	$70.65	$70.70
Purchase #4	$85.28	11.642%	$95.2083	$95.21	$95.20	$95.20
Purchase #5	$149.82	10.535%	$165.6035	$165.60	$165.60	$165.60
Purchase #6	$46.90	4.767%	$49.1357	$49.14	$49.15	$49.10
Purchase #7	$97.25	13.684%	$110.5577	$110.56	$110.55	$110.60
7 purchase totals =	$550.31		$605.8847	$605.88	$605.85	$605.90