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	$131.58	5.208%	$138.4327	$138.43	$138.45	$138.40
Purchase #2	$216.53	3.309%	$223.695	$223.70	$223.70	$223.70
Purchase #3	$91.86	8.833%	$99.974	$99.97	$99.95	$100.00
Purchase #4	$234.84	9.409%	$256.9361	$256.94	$256.95	$256.90
Purchase #5	$49.39	9.191%	$53.9294	$53.93	$53.95	$53.90
Purchase #6	$182.83	9.526%	$200.2464	$200.25	$200.25	$200.20
Purchase #7	$191.82	7.862%	$206.9009	$206.90	$206.90	$206.90
7 purchase totals =	$1,098.85		$1,180.1145	$1,180.12	$1,180.15	$1,180.00