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	$169.77	3.280%	$175.3385	$175.34	$175.35	$175.30
Purchase #2	$217.69	3.666%	$225.6705	$225.67	$225.65	$225.70
Purchase #3	$71.81	9.823%	$78.8639	$78.86	$78.85	$78.90
Purchase #4	$152.26	5.726%	$160.9784	$160.98	$161.00	$161.00
Purchase #5	$74.67	11.328%	$83.1286	$83.13	$83.15	$83.10
Purchase #6	$74.87	5.174%	$78.7438	$78.74	$78.75	$78.70
Purchase #7	$166.65	5.870%	$176.4324	$176.43	$176.45	$176.40
7 purchase totals =	$927.72		$979.1561	$979.15	$979.20	$979.10