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	$25.89	11.874%	$28.9642	$28.96	$28.95	$29.00
Purchase #2	$82.83	12.694%	$93.3444	$93.34	$93.35	$93.30
Purchase #3	$105.39	3.688%	$109.2768	$109.28	$109.30	$109.30
Purchase #4	$140.56	7.799%	$151.5223	$151.52	$151.50	$151.50
Purchase #5	$181.80	3.862%	$188.8211	$188.82	$188.80	$188.80
Purchase #6	$183.71	4.801%	$192.5299	$192.53	$192.55	$192.50
Purchase #7	$102.46	10.379%	$113.0943	$113.09	$113.10	$113.10
7 purchase totals =	$822.64		$877.5530	$877.54	$877.55	$877.50