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	$37.27	8.376%	$40.3917	$40.39	$40.40	$40.40
Purchase #2	$147.69	5.810%	$156.2708	$156.27	$156.25	$156.30
Purchase #3	$140.72	3.403%	$145.5087	$145.51	$145.50	$145.50
Purchase #4	$213.66	12.620%	$240.6239	$240.62	$240.60	$240.60
Purchase #5	$212.35	5.196%	$223.3837	$223.38	$223.40	$223.40
Purchase #6	$119.95	8.789%	$130.4924	$130.49	$130.50	$130.50
Purchase #7	$69.33	11.275%	$77.147	$77.15	$77.15	$77.10
7 purchase totals =	$940.97		$1,013.8182	$1,013.81	$1,013.80	$1,013.80