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	$233.89	11.843%	$261.5896	$261.59	$261.60	$261.60
Purchase #2	$150.45	6.739%	$160.5888	$160.59	$160.60	$160.60
Purchase #3	$208.56	6.712%	$222.5585	$222.56	$222.55	$222.60
Purchase #4	$89.38	12.689%	$100.7214	$100.72	$100.70	$100.70
Purchase #5	$185.43	7.841%	$199.9696	$199.97	$199.95	$200.00
Purchase #6	$172.85	3.400%	$178.7269	$178.73	$178.75	$178.70
Purchase #7	$5.90	13.830%	$6.716	$6.72	$6.70	$6.70
7 purchase totals =	$1,046.46		$1,130.8708	$1,130.88	$1,130.85	$1,130.90