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	$229.72	6.179%	$243.9144	$243.91	$243.90	$243.90
Purchase #2	$165.96	13.214%	$187.89	$187.89	$187.90	$187.90
Purchase #3	$39.66	12.206%	$44.5009	$44.50	$44.50	$44.50
Purchase #4	$198.54	5.486%	$209.4319	$209.43	$209.45	$209.40
Purchase #5	$159.97	10.320%	$176.4789	$176.48	$176.50	$176.50
Purchase #6	$207.69	11.250%	$231.0551	$231.06	$231.05	$231.10
Purchase #7	$81.86	6.686%	$87.3332	$87.33	$87.35	$87.30
7 purchase totals =	$1,083.40		$1,180.6044	$1,180.60	$1,180.65	$1,180.60