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	$126.66	12.252%	$142.1784	$142.18	$142.20	$142.20
Purchase #2	$109.41	9.359%	$119.6497	$119.65	$119.65	$119.60
Purchase #3	$99.95	3.386%	$103.3343	$103.33	$103.35	$103.30
Purchase #4	$36.32	8.509%	$39.4105	$39.41	$39.40	$39.40
Purchase #5	$162.50	13.873%	$185.0436	$185.04	$185.05	$185.00
Purchase #6	$36.74	9.461%	$40.216	$40.22	$40.20	$40.20
Purchase #7	$200.95	13.814%	$228.7092	$228.71	$228.70	$228.70
7 purchase totals =	$772.53		$858.5417	$858.54	$858.55	$858.40