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	$56.87	5.334%	$59.9034	$59.90	$59.90	$59.90
Purchase #2	$48.99	10.224%	$53.9987	$54.00	$54.00	$54.00
Purchase #3	$89.72	5.657%	$94.7955	$94.80	$94.80	$94.80
Purchase #4	$171.34	9.542%	$187.6893	$187.69	$187.70	$187.70
Purchase #5	$174.45	7.624%	$187.7501	$187.75	$187.75	$187.80
Purchase #6	$133.43	6.727%	$142.4058	$142.41	$142.40	$142.40
Purchase #7	$27.70	13.637%	$31.4774	$31.48	$31.50	$31.50
7 purchase totals =	$702.50		$758.0202	$758.03	$758.05	$758.10