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	$250.38	12.124%	$280.7361	$280.74	$280.75	$280.70
Purchase #2	$130.68	4.773%	$136.9174	$136.92	$136.90	$136.90
Purchase #3	$178.57	3.526%	$184.8664	$184.87	$184.85	$184.90
Purchase #4	$53.31	10.713%	$59.0211	$59.02	$59.00	$59.00
Purchase #5	$125.98	4.577%	$131.7461	$131.75	$131.75	$131.70
Purchase #6	$93.47	12.281%	$104.9491	$104.95	$104.95	$104.90
Purchase #7	$36.99	9.552%	$40.5233	$40.52	$40.50	$40.50
7 purchase totals =	$869.38		$938.7595	$938.77	$938.70	$938.60