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	$230.89	6.646%	$246.2349	$246.23	$246.25	$246.20
Purchase #2	$171.76	11.402%	$191.3441	$191.34	$191.35	$191.30
Purchase #3	$239.75	6.869%	$256.2184	$256.22	$256.20	$256.20
Purchase #4	$143.61	8.873%	$156.3525	$156.35	$156.35	$156.40
Purchase #5	$233.68	9.143%	$255.0454	$255.05	$255.05	$255.00
Purchase #6	$52.78	12.760%	$59.5147	$59.51	$59.50	$59.50
Purchase #7	$120.88	11.603%	$134.9057	$134.91	$134.90	$134.90
7 purchase totals =	$1,193.35		$1,299.6157	$1,299.61	$1,299.60	$1,299.50