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	$38.56	6.170%	$40.9392	$40.94	$40.95	$40.90
Purchase #2	$174.95	8.645%	$190.0744	$190.07	$190.05	$190.10
Purchase #3	$102.64	3.623%	$106.3586	$106.36	$106.35	$106.40
Purchase #4	$91.83	3.269%	$94.8319	$94.83	$94.85	$94.80
Purchase #5	$146.83	12.329%	$164.9327	$164.93	$164.95	$164.90
Purchase #6	$126.72	12.103%	$142.0569	$142.06	$142.05	$142.10
Purchase #7	$31.57	3.217%	$32.5856	$32.59	$32.60	$32.60
7 purchase totals =	$713.10		$771.7793	$771.78	$771.80	$771.80