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	$127.84	6.690%	$136.3925	$136.39	$136.40	$136.40
Purchase #2	$82.86	9.597%	$90.8121	$90.81	$90.80	$90.80
Purchase #3	$187.90	8.479%	$203.832	$203.83	$203.85	$203.80
Purchase #4	$39.98	12.641%	$45.0339	$45.03	$45.05	$45.00
Purchase #5	$96.59	9.555%	$105.8192	$105.82	$105.80	$105.80
Purchase #6	$106.98	7.748%	$115.2688	$115.27	$115.25	$115.30
Purchase #7	$75.63	4.187%	$78.7966	$78.80	$78.80	$78.80
7 purchase totals =	$717.78		$775.9551	$775.95	$775.95	$775.90