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	$147.71	5.271%	$155.4958	$155.50	$155.50	$155.50
Purchase #2	$64.62	10.671%	$71.5156	$71.52	$71.50	$71.50
Purchase #3	$94.77	8.562%	$102.8842	$102.88	$102.90	$102.90
Purchase #4	$86.51	12.563%	$97.3783	$97.38	$97.40	$97.40
Purchase #5	$76.38	5.340%	$80.4587	$80.46	$80.45	$80.50
Purchase #6	$67.34	10.536%	$74.4349	$74.43	$74.45	$74.40
Purchase #7	$185.49	5.813%	$196.2725	$196.27	$196.25	$196.30
7 purchase totals =	$722.82		$778.4400	$778.44	$778.45	$778.50