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	$17.46	5.510%	$18.422	$18.42	$18.40	$18.40
Purchase #2	$224.64	12.816%	$253.4299	$253.43	$253.45	$253.40
Purchase #3	$194.73	12.306%	$218.6935	$218.69	$218.70	$218.70
Purchase #4	$37.83	7.154%	$40.5364	$40.54	$40.55	$40.50
Purchase #5	$75.42	9.368%	$82.4853	$82.49	$82.50	$82.50
Purchase #6	$216.29	6.222%	$229.7476	$229.75	$229.75	$229.70
Purchase #7	$159.94	13.188%	$181.0329	$181.03	$181.05	$181.00
7 purchase totals =	$926.31		$1,024.3476	$1,024.35	$1,024.40	$1,024.20