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	$18.79	8.508%	$20.3887	$20.39	$20.40	$20.40
Purchase #2	$213.95	9.261%	$233.7639	$233.76	$233.75	$233.80
Purchase #3	$117.27	5.286%	$123.4689	$123.47	$123.45	$123.50
Purchase #4	$240.68	13.472%	$273.1044	$273.10	$273.10	$273.10
Purchase #5	$134.59	9.111%	$146.8525	$146.85	$146.85	$146.90
Purchase #6	$29.60	13.192%	$33.5048	$33.50	$33.50	$33.50
Purchase #7	$103.44	6.448%	$110.1098	$110.11	$110.10	$110.10
7 purchase totals =	$858.32		$941.1930	$941.18	$941.15	$941.30