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	$55.26	7.472%	$59.389	$59.39	$59.40	$59.40
Purchase #2	$204.48	5.396%	$215.5137	$215.51	$215.50	$215.50
Purchase #3	$23.79	13.797%	$27.0723	$27.07	$27.05	$27.10
Purchase #4	$98.46	3.135%	$101.5467	$101.55	$101.55	$101.50
Purchase #5	$42.69	10.786%	$47.2945	$47.29	$47.30	$47.30
Purchase #6	$148.59	13.640%	$168.8577	$168.86	$168.85	$168.90
Purchase #7	$14.88	12.817%	$16.7872	$16.79	$16.80	$16.80
7 purchase totals =	$588.15		$636.4611	$636.46	$636.45	$636.50