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	$65.27	3.187%	$67.3502	$67.35	$67.35	$67.40
Purchase #2	$60.67	12.818%	$68.4467	$68.45	$68.45	$68.40
Purchase #3	$46.38	9.404%	$50.7416	$50.74	$50.75	$50.70
Purchase #4	$237.66	12.566%	$267.5244	$267.52	$267.50	$267.50
Purchase #5	$166.61	5.255%	$175.3654	$175.37	$175.35	$175.40
Purchase #6	$53.62	11.755%	$59.923	$59.92	$59.90	$59.90
Purchase #7	$166.32	9.184%	$181.5948	$181.59	$181.60	$181.60
7 purchase totals =	$796.53		$870.9461	$870.94	$870.90	$870.90