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	$56.83	4.661%	$59.4788	$59.48	$59.50	$59.50
Purchase #2	$106.97	8.834%	$116.4197	$116.42	$116.40	$116.40
Purchase #3	$51.48	13.793%	$58.5806	$58.58	$58.60	$58.60
Purchase #4	$98.69	3.144%	$101.7928	$101.79	$101.80	$101.80
Purchase #5	$92.69	3.473%	$95.9091	$95.91	$95.90	$95.90
Purchase #6	$64.63	10.463%	$71.3922	$71.39	$71.40	$71.40
Purchase #7	$95.40	5.804%	$100.937	$100.94	$100.95	$100.90
7 purchase totals =	$566.69		$604.5102	$604.51	$604.55	$604.50