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	$29.84	9.225%	$32.5927	$32.59	$32.60	$32.60
Purchase #2	$243.99	6.716%	$260.3764	$260.38	$260.40	$260.40
Purchase #3	$39.97	13.154%	$45.2277	$45.23	$45.25	$45.20
Purchase #4	$148.29	11.411%	$165.2114	$165.21	$165.20	$165.20
Purchase #5	$87.72	13.131%	$99.2385	$99.24	$99.25	$99.20
Purchase #6	$218.90	3.474%	$226.5046	$226.50	$226.50	$226.50
Purchase #7	$51.74	6.112%	$54.9023	$54.90	$54.90	$54.90
7 purchase totals =	$820.45		$884.0536	$884.05	$884.10	$884.00