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	$150.63	5.855%	$159.4494	$159.45	$159.45	$159.40
Purchase #2	$158.27	4.315%	$165.0994	$165.10	$165.10	$165.10
Purchase #3	$194.85	9.775%	$213.8966	$213.90	$213.90	$213.90
Purchase #4	$151.69	3.835%	$157.5073	$157.51	$157.50	$157.50
Purchase #5	$31.46	7.689%	$33.879	$33.88	$33.90	$33.90
Purchase #6	$71.61	7.200%	$76.7659	$76.77	$76.75	$76.80
Purchase #7	$80.53	6.735%	$85.9537	$85.95	$85.95	$86.00
7 purchase totals =	$839.04		$892.5513	$892.56	$892.55	$892.60