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	$245.79	11.466%	$273.9723	$273.97	$273.95	$274.00
Purchase #2	$68.31	3.408%	$70.638	$70.64	$70.65	$70.60
Purchase #3	$94.99	5.653%	$100.3598	$100.36	$100.35	$100.40
Purchase #4	$60.43	11.663%	$67.478	$67.48	$67.50	$67.50
Purchase #5	$113.68	8.685%	$123.5531	$123.55	$123.55	$123.60
Purchase #6	$149.85	9.712%	$164.4034	$164.40	$164.40	$164.40
Purchase #7	$153.28	9.546%	$167.9121	$167.91	$167.90	$167.90
7 purchase totals =	$886.33		$968.3167	$968.31	$968.30	$968.40