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	$240.52	9.136%	$262.4939	$262.49	$262.50	$262.50
Purchase #2	$237.75	11.574%	$265.2672	$265.27	$265.25	$265.30
Purchase #3	$81.55	13.102%	$92.2347	$92.23	$92.25	$92.20
Purchase #4	$188.70	7.226%	$202.3355	$202.34	$202.35	$202.30
Purchase #5	$55.38	7.571%	$59.5728	$59.57	$59.55	$59.60
Purchase #6	$74.91	4.816%	$78.5177	$78.52	$78.50	$78.50
Purchase #7	$250.34	12.121%	$280.6837	$280.68	$280.70	$280.70
7 purchase totals =	$1,129.15		$1,241.1055	$1,241.10	$1,241.10	$1,241.10