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	$61.76	5.297%	$65.0314	$65.03	$65.05	$65.00
Purchase #2	$162.43	3.382%	$167.9234	$167.92	$167.90	$167.90
Purchase #3	$110.47	9.774%	$121.2673	$121.27	$121.25	$121.30
Purchase #4	$166.46	4.502%	$173.954	$173.95	$173.95	$174.00
Purchase #5	$57.26	13.397%	$64.9311	$64.93	$64.95	$64.90
Purchase #6	$83.54	7.377%	$89.7027	$89.70	$89.70	$89.70
Purchase #7	$82.56	3.712%	$85.6246	$85.62	$85.60	$85.60
7 purchase totals =	$724.48		$768.4345	$768.42	$768.40	$768.40