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	$84.30	6.618%	$89.879	$89.88	$89.90	$89.90
Purchase #2	$84.43	6.201%	$89.6655	$89.67	$89.65	$89.70
Purchase #3	$86.28	3.483%	$89.2851	$89.29	$89.30	$89.30
Purchase #4	$151.72	3.744%	$157.4004	$157.40	$157.40	$157.40
Purchase #5	$62.53	11.196%	$69.5309	$69.53	$69.55	$69.50
Purchase #6	$78.53	6.444%	$83.5905	$83.59	$83.60	$83.60
Purchase #7	$160.28	6.866%	$171.2848	$171.28	$171.30	$171.30
7 purchase totals =	$708.07		$750.6362	$750.64	$750.70	$750.70