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	$168.28	5.855%	$178.1328	$178.13	$178.15	$178.10
Purchase #2	$200.41	7.471%	$215.3826	$215.38	$215.40	$215.40
Purchase #3	$142.48	7.123%	$152.6289	$152.63	$152.65	$152.60
Purchase #4	$86.65	3.840%	$89.9774	$89.98	$90.00	$90.00
Purchase #5	$232.57	6.311%	$247.2475	$247.25	$247.25	$247.20
Purchase #6	$31.83	3.360%	$32.8995	$32.90	$32.90	$32.90
Purchase #7	$34.66	11.648%	$38.6972	$38.70	$38.70	$38.70
7 purchase totals =	$896.88		$954.9659	$954.97	$955.05	$954.90