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	$118.86	13.297%	$134.6648	$134.66	$134.65	$134.70
Purchase #2	$220.79	5.641%	$233.2448	$233.24	$233.25	$233.20
Purchase #3	$93.40	13.233%	$105.7596	$105.76	$105.75	$105.80
Purchase #4	$51.54	9.349%	$56.3585	$56.36	$56.35	$56.40
Purchase #5	$148.55	13.284%	$168.2834	$168.28	$168.30	$168.30
Purchase #6	$96.88	7.536%	$104.1809	$104.18	$104.20	$104.20
Purchase #7	$29.59	7.546%	$31.8229	$31.82	$31.80	$31.80
7 purchase totals =	$759.61		$834.3149	$834.30	$834.30	$834.40