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	$137.26	6.201%	$145.7715	$145.77	$145.75	$145.80
Purchase #2	$115.72	6.366%	$123.0867	$123.09	$123.10	$123.10
Purchase #3	$142.49	9.573%	$156.1306	$156.13	$156.15	$156.10
Purchase #4	$63.36	6.279%	$67.3384	$67.34	$67.35	$67.30
Purchase #5	$140.81	7.641%	$151.5693	$151.57	$151.55	$151.60
Purchase #6	$68.25	5.246%	$71.8304	$71.83	$71.85	$71.80
Purchase #7	$237.51	13.165%	$268.7782	$268.78	$268.80	$268.80
7 purchase totals =	$905.40		$984.5051	$984.51	$984.55	$984.50