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	$30.53	5.833%	$32.3108	$32.31	$32.30	$32.30
Purchase #2	$87.32	10.634%	$96.6056	$96.61	$96.60	$96.60
Purchase #3	$116.35	6.502%	$123.9151	$123.92	$123.90	$123.90
Purchase #4	$111.50	5.314%	$117.4251	$117.43	$117.45	$117.40
Purchase #5	$156.51	11.824%	$175.0157	$175.02	$175.00	$175.00
Purchase #6	$150.34	10.303%	$165.8295	$165.83	$165.85	$165.80
Purchase #7	$169.85	11.438%	$189.2774	$189.28	$189.30	$189.30
7 purchase totals =	$822.40		$900.3792	$900.40	$900.40	$900.30