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	$135.42	6.414%	$144.1058	$144.11	$144.10	$144.10
Purchase #2	$28.85	11.375%	$32.1317	$32.13	$32.15	$32.10
Purchase #3	$227.74	12.160%	$255.4332	$255.43	$255.45	$255.40
Purchase #4	$131.96	13.829%	$150.2087	$150.21	$150.20	$150.20
Purchase #5	$139.28	3.343%	$143.9361	$143.94	$143.95	$143.90
Purchase #6	$50.55	3.565%	$52.3521	$52.35	$52.35	$52.40
Purchase #7	$231.32	4.701%	$242.1944	$242.19	$242.20	$242.20
7 purchase totals =	$945.12		$1,020.3620	$1,020.36	$1,020.40	$1,020.30