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	$77.57	12.525%	$87.2856	$87.29	$87.30	$87.30
Purchase #2	$225.73	13.141%	$255.3932	$255.39	$255.40	$255.40
Purchase #3	$128.86	6.192%	$136.839	$136.84	$136.85	$136.80
Purchase #4	$71.33	13.124%	$80.6913	$80.69	$80.70	$80.70
Purchase #5	$36.75	7.400%	$39.4695	$39.47	$39.45	$39.50
Purchase #6	$250.81	11.773%	$280.3379	$280.34	$280.35	$280.30
Purchase #7	$116.48	11.234%	$129.5654	$129.57	$129.55	$129.60
7 purchase totals =	$907.53		$1,009.5819	$1,009.59	$1,009.60	$1,009.60