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	$95.57	8.286%	$103.4889	$103.49	$103.50	$103.50
Purchase #2	$80.88	10.254%	$89.1734	$89.17	$89.15	$89.20
Purchase #3	$37.41	6.373%	$39.7941	$39.79	$39.80	$39.80
Purchase #4	$125.90	9.800%	$138.2382	$138.24	$138.25	$138.20
Purchase #5	$200.81	7.835%	$216.5435	$216.54	$216.55	$216.50
Purchase #6	$73.38	10.229%	$80.886	$80.89	$80.90	$80.90
Purchase #7	$138.98	9.331%	$151.9482	$151.95	$151.95	$151.90
7 purchase totals =	$752.93		$820.0723	$820.07	$820.10	$820.00