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	$167.90	11.758%	$187.6417	$187.64	$187.65	$187.60
Purchase #2	$216.27	4.257%	$225.4766	$225.48	$225.50	$225.50
Purchase #3	$163.70	10.184%	$180.3712	$180.37	$180.35	$180.40
Purchase #4	$65.42	11.546%	$72.9734	$72.97	$72.95	$73.00
Purchase #5	$105.42	11.557%	$117.6034	$117.60	$117.60	$117.60
Purchase #6	$78.35	13.688%	$89.0745	$89.07	$89.05	$89.10
Purchase #7	$128.74	10.381%	$142.1045	$142.10	$142.10	$142.10
7 purchase totals =	$925.80		$1,015.2453	$1,015.23	$1,015.20	$1,015.30