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	$174.37	4.441%	$182.1138	$182.11	$182.10	$182.10
Purchase #2	$145.92	6.730%	$155.7404	$155.74	$155.75	$155.70
Purchase #3	$74.83	10.409%	$82.6191	$82.62	$82.60	$82.60
Purchase #4	$78.96	6.373%	$83.9921	$83.99	$84.00	$84.00
Purchase #5	$71.37	12.699%	$80.4333	$80.43	$80.45	$80.40
Purchase #6	$117.30	8.577%	$127.3608	$127.36	$127.35	$127.40
Purchase #7	$222.78	10.561%	$246.3078	$246.31	$246.30	$246.30
7 purchase totals =	$885.53		$958.5673	$958.56	$958.55	$958.50