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	$133.34	4.500%	$139.3403	$139.34	$139.35	$139.30
Purchase #2	$24.59	4.277%	$25.6417	$25.64	$25.65	$25.60
Purchase #3	$203.82	9.672%	$223.5335	$223.53	$223.55	$223.50
Purchase #4	$42.37	6.791%	$45.2473	$45.25	$45.25	$45.20
Purchase #5	$24.46	12.453%	$27.506	$27.51	$27.50	$27.50
Purchase #6	$93.85	8.606%	$101.9267	$101.93	$101.95	$101.90
Purchase #7	$26.73	3.268%	$27.6035	$27.60	$27.60	$27.60
7 purchase totals =	$549.16		$590.7990	$590.80	$590.85	$590.60