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	$75.90	6.232%	$80.6301	$80.63	$80.65	$80.60
Purchase #2	$129.72	12.469%	$145.8948	$145.89	$145.90	$145.90
Purchase #3	$166.47	11.423%	$185.4859	$185.49	$185.50	$185.50
Purchase #4	$244.67	8.636%	$265.7997	$265.80	$265.80	$265.80
Purchase #5	$149.32	8.250%	$161.6389	$161.64	$161.65	$161.60
Purchase #6	$103.98	13.331%	$117.8416	$117.84	$117.85	$117.80
Purchase #7	$48.78	7.705%	$52.5385	$52.54	$52.55	$52.50
7 purchase totals =	$918.84		$1,009.8295	$1,009.83	$1,009.90	$1,009.70