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	$52.82	6.475%	$56.2401	$56.24	$56.25	$56.20
Purchase #2	$198.59	12.869%	$224.1465	$224.15	$224.15	$224.10
Purchase #3	$16.86	10.194%	$18.5787	$18.58	$18.60	$18.60
Purchase #4	$135.76	4.871%	$142.3729	$142.37	$142.35	$142.40
Purchase #5	$142.42	3.512%	$147.4218	$147.42	$147.40	$147.40
Purchase #6	$74.88	9.503%	$81.9958	$82.00	$82.00	$82.00
Purchase #7	$180.45	9.152%	$196.9648	$196.96	$196.95	$197.00
7 purchase totals =	$801.78		$867.7206	$867.72	$867.70	$867.70