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	$67.30	6.188%	$71.4645	$71.46	$71.45	$71.50
Purchase #2	$244.74	13.778%	$278.4603	$278.46	$278.45	$278.50
Purchase #3	$146.89	13.247%	$166.3485	$166.35	$166.35	$166.30
Purchase #4	$123.52	10.548%	$136.5489	$136.55	$136.55	$136.50
Purchase #5	$51.56	9.661%	$56.5412	$56.54	$56.55	$56.50
Purchase #6	$246.91	3.639%	$255.8951	$255.90	$255.90	$255.90
Purchase #7	$49.47	6.197%	$52.5357	$52.54	$52.55	$52.50
7 purchase totals =	$930.39		$1,017.7942	$1,017.80	$1,017.80	$1,017.70