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	$61.89	9.122%	$67.5356	$67.54	$67.55	$67.50
Purchase #2	$152.54	3.638%	$158.0894	$158.09	$158.10	$158.10
Purchase #3	$130.50	4.438%	$136.2916	$136.29	$136.30	$136.30
Purchase #4	$128.43	7.442%	$137.9878	$137.99	$138.00	$138.00
Purchase #5	$134.86	5.561%	$142.3596	$142.36	$142.35	$142.40
Purchase #6	$40.57	12.839%	$45.7788	$45.78	$45.80	$45.80
Purchase #7	$179.31	7.360%	$192.5072	$192.51	$192.50	$192.50
7 purchase totals =	$828.10		$880.5500	$880.56	$880.60	$880.60