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	$146.57	9.191%	$160.0412	$160.04	$160.05	$160.00
Purchase #2	$210.40	5.815%	$222.6348	$222.63	$222.65	$222.60
Purchase #3	$36.31	7.285%	$38.9552	$38.96	$38.95	$39.00
Purchase #4	$240.87	3.543%	$249.404	$249.40	$249.40	$249.40
Purchase #5	$81.28	11.401%	$90.5467	$90.55	$90.55	$90.50
Purchase #6	$11.42	4.260%	$11.9065	$11.91	$11.90	$11.90
Purchase #7	$24.96	10.303%	$27.5316	$27.53	$27.55	$27.50
7 purchase totals =	$751.81		$801.0200	$801.02	$801.05	$800.90