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	$112.40	10.626%	$124.3436	$124.34	$124.35	$124.30
Purchase #2	$146.70	13.372%	$166.3167	$166.32	$166.30	$166.30
Purchase #3	$18.34	6.535%	$19.5385	$19.54	$19.55	$19.50
Purchase #4	$79.71	10.597%	$88.1569	$88.16	$88.15	$88.20
Purchase #5	$28.57	12.607%	$32.1718	$32.17	$32.15	$32.20
Purchase #6	$110.50	11.800%	$123.539	$123.54	$123.55	$123.50
Purchase #7	$67.92	7.792%	$73.2123	$73.21	$73.20	$73.20
7 purchase totals =	$564.14		$627.2788	$627.28	$627.25	$627.20