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	$63.48	3.277%	$65.5602	$65.56	$65.55	$65.60
Purchase #2	$39.83	12.380%	$44.761	$44.76	$44.75	$44.80
Purchase #3	$100.38	3.159%	$103.551	$103.55	$103.55	$103.60
Purchase #4	$17.33	3.771%	$17.9835	$17.98	$18.00	$18.00
Purchase #5	$96.63	9.451%	$105.7625	$105.76	$105.75	$105.80
Purchase #6	$129.79	9.799%	$142.5081	$142.51	$142.50	$142.50
Purchase #7	$147.52	10.183%	$162.542	$162.54	$162.55	$162.50
7 purchase totals =	$594.96		$642.6683	$642.66	$642.65	$642.80