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	$29.73	5.181%	$31.2703	$31.27	$31.25	$31.30
Purchase #2	$184.79	13.322%	$209.4077	$209.41	$209.40	$209.40
Purchase #3	$91.41	8.226%	$98.9294	$98.93	$98.95	$98.90
Purchase #4	$10.96	13.695%	$12.461	$12.46	$12.45	$12.50
Purchase #5	$5.39	4.750%	$5.646	$5.65	$5.65	$5.60
Purchase #6	$230.25	3.602%	$238.5436	$238.54	$238.55	$238.50
Purchase #7	$82.33	12.158%	$92.3397	$92.34	$92.35	$92.30
7 purchase totals =	$634.86		$688.5977	$688.60	$688.60	$688.50