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	$7.62	9.400%	$8.3363	$8.34	$8.35	$8.30
Purchase #2	$39.33	10.516%	$43.4659	$43.47	$43.45	$43.50
Purchase #3	$127.81	6.731%	$136.4129	$136.41	$136.40	$136.40
Purchase #4	$158.72	6.218%	$168.5892	$168.59	$168.60	$168.60
Purchase #5	$179.31	6.809%	$191.5192	$191.52	$191.50	$191.50
Purchase #6	$42.33	13.593%	$48.0839	$48.08	$48.10	$48.10
Purchase #7	$242.77	4.861%	$254.571	$254.57	$254.55	$254.60
7 purchase totals =	$797.89		$850.9784	$850.98	$850.95	$851.00