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	$17.74	6.856%	$18.9563	$18.96	$18.95	$19.00
Purchase #2	$186.32	10.602%	$206.0736	$206.07	$206.05	$206.10
Purchase #3	$68.93	4.623%	$72.1166	$72.12	$72.10	$72.10
Purchase #4	$22.25	10.362%	$24.5555	$24.56	$24.55	$24.60
Purchase #5	$33.70	10.515%	$37.2436	$37.24	$37.25	$37.20
Purchase #6	$44.63	13.511%	$50.66	$50.66	$50.65	$50.70
Purchase #7	$118.33	7.528%	$127.2379	$127.24	$127.25	$127.20
7 purchase totals =	$491.90		$536.8435	$536.85	$536.80	$536.90