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	$228.56	12.203%	$256.4512	$256.45	$256.45	$256.50
Purchase #2	$220.53	5.835%	$233.3979	$233.40	$233.40	$233.40
Purchase #3	$174.73	7.738%	$188.2506	$188.25	$188.25	$188.30
Purchase #4	$66.79	6.864%	$71.3745	$71.37	$71.35	$71.40
Purchase #5	$236.26	13.818%	$268.9064	$268.91	$268.90	$268.90
Purchase #6	$112.49	4.166%	$117.1763	$117.18	$117.20	$117.20
Purchase #7	$142.89	13.782%	$162.5831	$162.58	$162.60	$162.60
7 purchase totals =	$1,182.25		$1,298.1400	$1,298.14	$1,298.15	$1,298.30