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	$105.92	5.551%	$111.7996	$111.80	$111.80	$111.80
Purchase #2	$37.52	11.266%	$41.747	$41.75	$41.75	$41.70
Purchase #3	$79.48	8.698%	$86.3932	$86.39	$86.40	$86.40
Purchase #4	$128.51	3.528%	$133.0438	$133.04	$133.05	$133.00
Purchase #5	$250.29	8.597%	$271.8074	$271.81	$271.80	$271.80
Purchase #6	$52.32	3.850%	$54.3343	$54.33	$54.35	$54.30
Purchase #7	$103.34	5.192%	$108.7054	$108.71	$108.70	$108.70
7 purchase totals =	$757.38		$807.8307	$807.83	$807.85	$807.70