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	$218.41	9.576%	$239.3249	$239.32	$239.30	$239.30
Purchase #2	$35.50	6.871%	$37.9392	$37.94	$37.95	$37.90
Purchase #3	$153.37	13.345%	$173.8372	$173.84	$173.85	$173.80
Purchase #4	$78.64	13.858%	$89.5379	$89.54	$89.55	$89.50
Purchase #5	$88.85	11.743%	$99.2837	$99.28	$99.30	$99.30
Purchase #6	$221.66	5.547%	$233.9555	$233.96	$233.95	$234.00
Purchase #7	$106.44	13.797%	$121.1255	$121.13	$121.15	$121.10
7 purchase totals =	$902.87		$995.0039	$995.01	$995.05	$994.90