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	$100.98	8.507%	$109.5704	$109.57	$109.55	$109.60
Purchase #2	$120.69	3.189%	$124.5388	$124.54	$124.55	$124.50
Purchase #3	$175.77	5.490%	$185.4198	$185.42	$185.40	$185.40
Purchase #4	$74.69	3.749%	$77.4901	$77.49	$77.50	$77.50
Purchase #5	$135.73	6.288%	$144.2647	$144.26	$144.25	$144.30
Purchase #6	$150.29	10.755%	$166.4537	$166.45	$166.45	$166.50
Purchase #7	$43.89	7.237%	$47.0663	$47.07	$47.05	$47.10
7 purchase totals =	$802.04		$854.8038	$854.80	$854.75	$854.90