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	$55.42	6.418%	$58.9769	$58.98	$59.00	$59.00
Purchase #2	$37.90	9.289%	$41.4205	$41.42	$41.40	$41.40
Purchase #3	$120.51	13.138%	$136.3426	$136.34	$136.35	$136.30
Purchase #4	$122.98	10.853%	$136.327	$136.33	$136.35	$136.30
Purchase #5	$225.89	12.844%	$254.9033	$254.90	$254.90	$254.90
Purchase #6	$158.31	12.780%	$178.542	$178.54	$178.55	$178.50
Purchase #7	$138.45	3.229%	$142.9206	$142.92	$142.90	$142.90
7 purchase totals =	$859.46		$949.4329	$949.43	$949.45	$949.30