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	$238.54	12.485%	$268.3217	$268.32	$268.30	$268.30
Purchase #2	$114.64	5.127%	$120.5176	$120.52	$120.50	$120.50
Purchase #3	$60.85	3.196%	$62.7948	$62.79	$62.80	$62.80
Purchase #4	$24.40	4.660%	$25.537	$25.54	$25.55	$25.50
Purchase #5	$168.42	10.671%	$186.3921	$186.39	$186.40	$186.40
Purchase #6	$104.26	4.673%	$109.1321	$109.13	$109.15	$109.10
Purchase #7	$36.72	4.220%	$38.2696	$38.27	$38.25	$38.30
7 purchase totals =	$747.83		$810.9649	$810.96	$810.95	$810.90