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	$229.83	6.709%	$245.2493	$245.25	$245.25	$245.20
Purchase #2	$75.70	12.392%	$85.0807	$85.08	$85.10	$85.10
Purchase #3	$95.52	9.580%	$104.6708	$104.67	$104.65	$104.70
Purchase #4	$135.95	3.491%	$140.696	$140.70	$140.70	$140.70
Purchase #5	$101.85	11.194%	$113.2511	$113.25	$113.25	$113.30
Purchase #6	$220.80	8.847%	$240.3342	$240.33	$240.35	$240.30
Purchase #7	$155.54	10.149%	$171.3258	$171.33	$171.35	$171.30
7 purchase totals =	$1,015.19		$1,100.6079	$1,100.61	$1,100.65	$1,100.60