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	$121.75	4.580%	$127.3262	$127.33	$127.35	$127.30
Purchase #2	$176.98	3.400%	$182.9973	$183.00	$183.00	$183.00
Purchase #3	$37.63	9.746%	$41.2974	$41.30	$41.30	$41.30
Purchase #4	$156.94	7.438%	$168.6132	$168.61	$168.60	$168.60
Purchase #5	$36.62	6.122%	$38.8619	$38.86	$38.85	$38.90
Purchase #6	$180.90	5.533%	$190.9092	$190.91	$190.90	$190.90
Purchase #7	$138.57	8.501%	$150.3498	$150.35	$150.35	$150.30
7 purchase totals =	$849.39		$900.3550	$900.36	$900.35	$900.30