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	$245.98	4.139%	$256.1611	$256.16	$256.15	$256.20
Purchase #2	$57.82	3.686%	$59.9512	$59.95	$59.95	$60.00
Purchase #3	$204.76	13.199%	$231.7863	$231.79	$231.80	$231.80
Purchase #4	$144.91	5.162%	$152.3903	$152.39	$152.40	$152.40
Purchase #5	$119.30	9.426%	$130.5452	$130.55	$130.55	$130.50
Purchase #6	$45.81	13.195%	$51.8546	$51.85	$51.85	$51.90
Purchase #7	$55.78	13.711%	$63.428	$63.43	$63.45	$63.40
7 purchase totals =	$874.36		$946.1167	$946.12	$946.15	$946.20