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	$108.28	6.688%	$115.5218	$115.52	$115.50	$115.50
Purchase #2	$99.83	3.387%	$103.2112	$103.21	$103.20	$103.20
Purchase #3	$248.36	5.463%	$261.9279	$261.93	$261.95	$261.90
Purchase #4	$28.90	10.501%	$31.9348	$31.93	$31.95	$31.90
Purchase #5	$46.82	10.738%	$51.8475	$51.85	$51.85	$51.80
Purchase #6	$41.56	3.335%	$42.946	$42.95	$42.95	$42.90
Purchase #7	$44.53	5.318%	$46.8981	$46.90	$46.90	$46.90
7 purchase totals =	$618.28		$654.2873	$654.29	$654.30	$654.10