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	$29.69	11.801%	$33.1937	$33.19	$33.20	$33.20
Purchase #2	$77.88	5.687%	$82.309	$82.31	$82.30	$82.30
Purchase #3	$195.28	12.231%	$219.1647	$219.16	$219.15	$219.20
Purchase #4	$138.98	9.709%	$152.4736	$152.47	$152.45	$152.50
Purchase #5	$156.33	6.530%	$166.5383	$166.54	$166.55	$166.50
Purchase #6	$70.65	11.713%	$78.9252	$78.93	$78.95	$78.90
Purchase #7	$210.26	8.143%	$227.3815	$227.38	$227.40	$227.40
7 purchase totals =	$879.07		$959.9860	$959.98	$960.00	$960.00