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	$141.76	11.682%	$158.3204	$158.32	$158.30	$158.30
Purchase #2	$191.99	12.504%	$215.9964	$216.00	$216.00	$216.00
Purchase #3	$36.36	10.727%	$40.2603	$40.26	$40.25	$40.30
Purchase #4	$177.61	4.221%	$185.1069	$185.11	$185.10	$185.10
Purchase #5	$112.72	10.592%	$124.6593	$124.66	$124.65	$124.70
Purchase #6	$245.58	6.492%	$261.5231	$261.52	$261.50	$261.50
Purchase #7	$128.78	6.649%	$137.3426	$137.34	$137.35	$137.30
7 purchase totals =	$1,034.80		$1,123.2090	$1,123.21	$1,123.15	$1,123.20