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	$165.89	13.184%	$187.7609	$187.76	$187.75	$187.80
Purchase #2	$232.87	8.538%	$252.7524	$252.75	$252.75	$252.80
Purchase #3	$221.40	4.407%	$231.1571	$231.16	$231.15	$231.20
Purchase #4	$38.89	9.365%	$42.532	$42.53	$42.55	$42.50
Purchase #5	$182.29	4.466%	$190.4311	$190.43	$190.45	$190.40
Purchase #6	$123.53	13.721%	$140.4796	$140.48	$140.50	$140.50
Purchase #7	$93.61	7.110%	$100.2657	$100.27	$100.25	$100.30
7 purchase totals =	$1,058.48		$1,145.3788	$1,145.38	$1,145.40	$1,145.50