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	$160.53	7.461%	$172.5071	$172.51	$172.50	$172.50
Purchase #2	$153.99	5.300%	$162.1515	$162.15	$162.15	$162.20
Purchase #3	$104.82	10.387%	$115.7077	$115.71	$115.70	$115.70
Purchase #4	$29.56	9.448%	$32.3528	$32.35	$32.35	$32.40
Purchase #5	$80.45	11.296%	$89.5376	$89.54	$89.55	$89.50
Purchase #6	$92.42	3.575%	$95.724	$95.72	$95.70	$95.70
Purchase #7	$167.51	8.850%	$182.3346	$182.33	$182.35	$182.30
7 purchase totals =	$789.28		$850.3153	$850.31	$850.30	$850.30