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	$152.46	13.582%	$173.1671	$173.17	$173.15	$173.20
Purchase #2	$162.63	3.679%	$168.6132	$168.61	$168.60	$168.60
Purchase #3	$150.76	10.815%	$167.0647	$167.06	$167.05	$167.10
Purchase #4	$66.60	8.654%	$72.3636	$72.36	$72.35	$72.40
Purchase #5	$46.95	7.339%	$50.3957	$50.40	$50.40	$50.40
Purchase #6	$93.50	5.863%	$98.9819	$98.98	$99.00	$99.00
Purchase #7	$94.36	9.325%	$103.1591	$103.16	$103.15	$103.20
7 purchase totals =	$767.26		$833.7453	$833.74	$833.70	$833.90