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	$77.79	13.817%	$88.5382	$88.54	$88.55	$88.50
Purchase #2	$154.87	6.496%	$164.9304	$164.93	$164.95	$164.90
Purchase #3	$150.31	9.122%	$164.0213	$164.02	$164.00	$164.00
Purchase #4	$178.31	3.695%	$184.8986	$184.90	$184.90	$184.90
Purchase #5	$40.29	11.377%	$44.8738	$44.87	$44.85	$44.90
Purchase #6	$68.82	11.182%	$76.5155	$76.52	$76.50	$76.50
Purchase #7	$238.65	8.764%	$259.5653	$259.57	$259.55	$259.60
7 purchase totals =	$909.04		$983.3431	$983.35	$983.30	$983.30