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	$75.34	3.660%	$78.0974	$78.10	$78.10	$78.10
Purchase #2	$40.66	9.490%	$44.5186	$44.52	$44.50	$44.50
Purchase #3	$179.83	9.855%	$197.5522	$197.55	$197.55	$197.60
Purchase #4	$233.62	4.407%	$243.9156	$243.92	$243.90	$243.90
Purchase #5	$137.99	3.114%	$142.287	$142.29	$142.30	$142.30
Purchase #6	$25.31	10.354%	$27.9306	$27.93	$27.95	$27.90
Purchase #7	$77.77	11.302%	$86.5596	$86.56	$86.55	$86.60
7 purchase totals =	$770.52		$820.8610	$820.87	$820.85	$820.90