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	$73.28	5.732%	$77.4804	$77.48	$77.50	$77.50
Purchase #2	$204.57	5.139%	$215.0829	$215.08	$215.10	$215.10
Purchase #3	$249.34	3.477%	$258.0096	$258.01	$258.00	$258.00
Purchase #4	$115.81	6.692%	$123.56	$123.56	$123.55	$123.60
Purchase #5	$106.39	3.259%	$109.8573	$109.86	$109.85	$109.90
Purchase #6	$129.89	6.254%	$138.0133	$138.01	$138.00	$138.00
Purchase #7	$48.74	7.726%	$52.5057	$52.51	$52.50	$52.50
7 purchase totals =	$928.02		$974.5092	$974.51	$974.50	$974.60