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	$94.54	12.546%	$106.401	$106.40	$106.40	$106.40
Purchase #2	$224.45	11.661%	$250.6231	$250.62	$250.60	$250.60
Purchase #3	$73.25	5.780%	$77.4839	$77.48	$77.50	$77.50
Purchase #4	$82.32	9.732%	$90.3314	$90.33	$90.35	$90.30
Purchase #5	$14.78	13.705%	$16.8056	$16.81	$16.80	$16.80
Purchase #6	$52.81	4.571%	$55.2239	$55.22	$55.20	$55.20
Purchase #7	$228.62	12.186%	$256.4796	$256.48	$256.50	$256.50
7 purchase totals =	$770.77		$853.3485	$853.34	$853.35	$853.30