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	$39.43	9.728%	$43.2658	$43.27	$43.25	$43.30
Purchase #2	$180.35	10.264%	$198.8611	$198.86	$198.85	$198.90
Purchase #3	$153.86	13.370%	$174.4311	$174.43	$174.45	$174.40
Purchase #4	$162.39	4.294%	$169.363	$169.36	$169.35	$169.40
Purchase #5	$219.86	5.435%	$231.8094	$231.81	$231.80	$231.80
Purchase #6	$11.38	9.308%	$12.4393	$12.44	$12.45	$12.40
Purchase #7	$62.69	13.826%	$71.3575	$71.36	$71.35	$71.40
7 purchase totals =	$829.96		$901.5272	$901.53	$901.50	$901.60