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	$14.51	5.216%	$15.2668	$15.27	$15.25	$15.30
Purchase #2	$194.95	13.771%	$221.7966	$221.80	$221.80	$221.80
Purchase #3	$76.72	11.496%	$85.5397	$85.54	$85.55	$85.50
Purchase #4	$76.64	8.492%	$83.1483	$83.15	$83.15	$83.10
Purchase #5	$27.68	13.347%	$31.3744	$31.37	$31.35	$31.40
Purchase #6	$103.27	12.300%	$115.9722	$115.97	$115.95	$116.00
Purchase #7	$64.66	4.183%	$67.3647	$67.36	$67.35	$67.40
7 purchase totals =	$558.43		$620.4627	$620.46	$620.40	$620.50