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	$166.91	7.528%	$179.475	$179.48	$179.50	$179.50
Purchase #2	$198.68	12.129%	$222.7779	$222.78	$222.80	$222.80
Purchase #3	$126.28	12.210%	$141.6988	$141.70	$141.70	$141.70
Purchase #4	$100.90	13.821%	$114.8454	$114.85	$114.85	$114.80
Purchase #5	$133.91	8.657%	$145.5026	$145.50	$145.50	$145.50
Purchase #6	$66.77	10.272%	$73.6286	$73.63	$73.65	$73.60
Purchase #7	$38.71	4.782%	$40.5611	$40.56	$40.55	$40.60
7 purchase totals =	$832.16		$918.4894	$918.50	$918.55	$918.50