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	$167.54	7.155%	$179.5275	$179.53	$179.55	$179.50
Purchase #2	$141.98	11.163%	$157.8292	$157.83	$157.85	$157.80
Purchase #3	$100.95	10.374%	$111.4226	$111.42	$111.40	$111.40
Purchase #4	$56.84	11.401%	$63.3203	$63.32	$63.30	$63.30
Purchase #5	$36.60	10.757%	$40.5371	$40.54	$40.55	$40.50
Purchase #6	$61.61	3.193%	$63.5772	$63.58	$63.60	$63.60
Purchase #7	$58.36	3.473%	$60.3868	$60.39	$60.40	$60.40
7 purchase totals =	$623.88		$676.6007	$676.61	$676.65	$676.50