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	$247.69	10.816%	$274.4802	$274.48	$274.50	$274.50
Purchase #2	$84.35	6.159%	$89.5451	$89.55	$89.55	$89.50
Purchase #3	$65.64	7.280%	$70.4186	$70.42	$70.40	$70.40
Purchase #4	$128.82	12.751%	$145.2458	$145.25	$145.25	$145.20
Purchase #5	$31.42	9.404%	$34.3747	$34.37	$34.35	$34.40
Purchase #6	$134.95	4.626%	$141.1928	$141.19	$141.20	$141.20
Purchase #7	$40.63	12.865%	$45.857	$45.86	$45.85	$45.90
7 purchase totals =	$733.50		$801.1142	$801.12	$801.10	$801.10