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	$31.79	7.131%	$34.0569	$34.06	$34.05	$34.10
Purchase #2	$38.74	5.658%	$40.9319	$40.93	$40.95	$40.90
Purchase #3	$210.34	12.216%	$236.0351	$236.04	$236.05	$236.00
Purchase #4	$40.78	3.677%	$42.2795	$42.28	$42.30	$42.30
Purchase #5	$62.66	11.840%	$70.0789	$70.08	$70.10	$70.10
Purchase #6	$178.77	12.147%	$200.4852	$200.49	$200.50	$200.50
Purchase #7	$109.48	7.460%	$117.6472	$117.65	$117.65	$117.60
7 purchase totals =	$672.56		$741.5147	$741.53	$741.60	$741.50